Figure 1. Classical omega-3 and omega-6 fatty acid synthesis pathways and the role of omega-3 fatty acids in regulating health/disease markers
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This document is in the public domain and may be used and reprinted without permission except those copyrighted materials noted for which further reproduction is prohibited without the specific permission of copyright holders.
This report is based on research conducted by the University of Ottawa Evidence-based Practice Center (EPC), under contract to the Agency for Healthcare Research and Quality (AHRQ), Rockville, MD (Contract No. 290-02-0021). The findings and conclusions in this document are those of the authors, who are responsible for its contents; the findings and conclusions do not necessarily represent the views of AHRQ. Therefore, no statement in this report should be construed as an official position of AHRQ or of the U.S. Department of Health and Human Services.
The information in this report is intended to help health care decisionmakers, patients and clinicians, health system leaders, and policymakers make well-informed decisions and thereby improve the quality of health care services. This report is not intended to be a substitute for the application of clinical judgment. Anyone who makes decisions concerning the provision of clinical care should consider this report as they would any medical reference and in conjunction with all other pertinent information, i.e., in the context of available resources and circumstances presented by individual patients.
This report may be used, in whole or in part, as the basis for development of clinical practice guidelines and other quality enhancement tools, or as a basis for reimbursement and coverage policies. Neither AHRQ's nor the U.S. Department of Health and Human Services' endorsement of such derivative products may be stated or implied.
Suggested Citation:
Lewin GA, Schachter HM, Yuen D, Merchant P, Mamaladze V, Tsertsvadze A, et al. Effects of Omega-3 Fatty Acids on Child and Maternal Health. Evidence Report/Technology Assessment No. 118. (Prepared by the University of Ottawa Evidence-based Practice Center, under Contract No. 290-02-0021.) AHRQ Publication No. 05-E025-2. Rockville, MD: Agency for Healthcare Research and Quality. August 2005.
The Agency for Healthcare Research and Quality(AHRQ), through its Evidence-Based Practice Centers(EPCs), sponsors the development of evidence reports and technology assessments to assist public- and private-sector organizations in their efforts to improve the quality of health care in the United States. This report was requested and funded by the Office of Dietary Supplements, National Institutes of Health. The reports and assessments provide organizations with comprehensive, science-based information on common, costly medical conditions and new health care technologies. The EPCs systematically review the relevant scientific literature on topics assigned to them by AHRQ and conduct additional analyses when appropriate prior to developing their reports and assessments.
To bring the broadest range of experts into the development of evidence reports and health technology assessments, AHRQ encourages the EPCs to form partnerships and enter into collaborations with other medical and research organizations. The EPCs work with these partner organizations to ensure that the evidence reports and technology assessments they produce will become building blocks for health care quality improvement projects throughout the Nation. The reports undergo peer review prior to their release.
AHRQ expects that the EPC evidence reports and technology assessments will inform individual health plans, providers, and purchasers as well as the health care system as a whole by providing important information to help improve health care quality.
We welcome comments on this evidence report. They may be sent by mail to the Task Order Officer named below at: Agency for Healthcare Research and Quality, 540 Gaither Road, Rockville, MD 20850, or by email to epc@ahrq.gov.
Carolyn M Clancy, M.D.
Director
Agency for Healthcare Resesarch and Quality
Paul Coates, Ph.D.
Director
Office of Dietary Supplements
National Institutes of Health
Jean Slutsky, P.A., M.S.P.H.
Director
Center for Outcomes and Evidence
Agency for Healthcare Research and Quality
Kenneth S. Fink, M.D., M.G.A., M.P.H.
Director, EPC Program
Agency for Healthcare Research and Quality
Beth A. Collins-Sharp, R.N.,Ph.D.
EPC Program Task Order Officer
Agency for Healthcare Research and Quality
The authors would like to thank numerous individuals for their support of the present project: our collaborators at SC-RAND and Tufts-NEMC EPCs; Isabella Steffensen and Christine Murray for their ability to convey with words, tables and figures what it is we did and found; for their expert and timely translation of articles; Herb Woolf for responding with substance to our request of industry for evidence; Peter O'Blenis for assuring that our software would adapt and grow as quickly as the project requirements shifted and expanded; Mary Fewtrell; Sjurdur Frodi Olsen; Maria Makrides; Eileen Birch; Susan Carlson for timely responded to our requests to clarify their research; Khai Tran and Maia Miguelez, PhD for providing input on the data abstraction forms; Nancy Santesso for helping on the development of the search strategy; Raymond Daniel for helping to retrieve the hard copies of the studies, Manijeh Hamifard for helping on the data abstraction and Chantelle Garritty for coordinating the project.
Context: The likely significance of omega-3 fatty acids for child and maternal health is therefore suggested by the observations that: the human brain and retina each contain considerable omega-3 fatty acid content; the child delivered at term receives and important supply of omega-3 fatty acids especially in the third trimester of pregnancy; and, due to a shortened gestational period, the child delivered prematurely receives less exposure to omega-3 fatty acid content than does the term child. This evidence is systematically reviewed there.
Objectives: The purpose of this study was to conduct a systematic review of the scientific-medical literature to identify, appraise and synthesize the evidence of omega-3 fatty acids in child and maternal health. Evidence was sought to investigate a series of questions regarding the influence of the omega-3 fatty acid intake (supplemented during pregnancy) on the duration of gestation, incidence of preeclampsia, eclapmsia or gestational hypertension (GHT), and incidence of infants small for gestational age (SGA), as well as the association between the maternal biomarkers during pregnancy and the pregnancy outcomes outlined above. The influence of the omega-3 fatty acid intake (supplemented or breast milk) on the developmental outcomes in preterm and term infants, such was growth, neurocognitive development and visual function, were also investigated, as well as the association between the maternal, fetal or child's biomarkers and these clinical outcomes. The impact of effect modifiers was also examined, as well as the safety profile. The results will be sued to inform a research agenda.
Data Sources: A comprehensive search for citations was conducted using five electronic databases (MEDLINE®, PreMEDLINE®, EMBASE, Cochrane Central Register of Controlled Trials, and CAB Health). Searches were not restricted by language of publication, publication type, or study design, except with respect to the MeSH term “dietary fats,” which was limited by study design to increase its specificity. Search elements included scientific terms (with acronyms), generic and trade names relating to the exposure and its sources (e.g., preterm, term, child development, etc). Additional published or unpublished literature was sought through manual searches of references lists of included studies and key review articles, and from the files of content experts.
Study Selection: Studies were considered relevant if they described live human populations of healthy preterm (<37 weeks of GA), term (>37 weeks of GA) infants of healthy pregnant women, investigated the use of any supplements (formula, diet, etc.) known to contain omega-3 fatty acids and/or human milk, and utilizing pertinent pregnancy and child developmental outcomes (e.g., growth, neurocognitive, visual). Studies examining the questions concerning the efficacy had to employ a controlled research design (i.e., RCTs), whereas, any type of design other than case-series or case-study was permitted to address the possible association between the content of biomarkers and the clinical outcomes. Three levels of screening for relevance, and two reviewers per level, were employed. Disagreements were resolved by consensus and, if necessary, third-party intervention.
Data Extraction: All data were extracted by one reviewer, then verified by a second one. Data included the characteristics of the report, study population, intervention/exposure and comparator(s), cointerventions, discontinuations (with reasons), and outcomes (i.e., clinical, biomarkers, safety). Study quality (internal validity) and study applicability (external validity) were appraised.
Data Synthesis: Question-specific qualitative synthesis of the evidence was derived. Meta-analysis was conducted with data concerning the supplemental influence on incidence of premature deliveries, GHT, birth weight, incidence of IUGR, growth patterns, (i.e., weight, length and head circumference) in term and preterm infants, neurological and cognitive development in term infants, and visual function in both term and preterm infants. One hundred and seventeen reports, describing 89 studies, were deemed relevant for the systematic review, with many studies described in more that one question.
Conclusions: Studies investigating the influence of omega-3 fatty acids on child and maternal health revealed the absence of a notable safety profile (i.e., moderate-to-severe AEs). Pregnancy outcomes were either unaffected by omega-3 fatty acid supplementation, or the results were inconclusive. Results suggested the absence of effects with respect to the impact of supplementation on the incidence of GHT, preeclampsia or eclampsia, as well as on infants being born SGA. However, regarding evaluations of the duration of gestation, some discrepancies were observed, although most of the studies failed to detect a statistically significant effect. Biomarker data failed to clarify patterns in pregnancy outcome data.
Results concerning the impact of the intake of omega-3 fatty acids on the development of infants are primarily, although not uniformly, inconclusive. The inconsistencies in study results may be attributable to numerous factors.
In addition, making clear sense of the absolute or relative effects of individual omega-3 fatty acids, or even omega-3 fatty acid combinations, on child outcomes is complicated or precluded by the following problem. Studies typically employed interventions that involved various cointerventional or background constituents (e.g., omega-6 fatty acids), yet whose metabolic interactions with the omega-3 fatty acid(s) were not taken into account in interpreting the results. The dynamic interplay among these fatty acid contents (e.g., competition for enzymes), and how this interplay may influence outcomes, may differ in important ways depending on whether DHA or olive oil is added to the combination of cointerventional or background constituents, particularly in the maternal population. This strategy prevented the isolation of the exact effects relating to the omega-3 fatty acid content. It is thus very difficult to reliably ascribe definite child outcome-related benefits, or the absence thereof, to specific omega-3 fatty acids. Biomarker data failed to clarify patterns in child outcome data.
Future research should likely consider investigating the impact of specific omega-6/omega-3 fatty acid intake ratios, in no small part to control for the possible metabolic interactions involving these types of fatty acids. To produce results that are applicable to the North American population, populations consuming high omega-6/omega-3 fatty acid intake ratios should likely be randomized into trials also exhibiting better control of confounding variables than was observed, especially in the present collection of studies of child outcomes.
This evidence report by the University of Ottawa's Evidence-Based Practice Center (EPC) concerning the effects of omega-3 fatty acids on child and maternal health is one among several that address topics related to omega-3 fatty acids that were requested and funded by the Office of Dietary Supplements, National Institutes of Health (NIH), through the EPC program at the Agency for Healthcare Research and Quality (AHRQ). Three EPCs—the Tufts-New England Medical Center (Tufts-NEMC) EPC, the Southern California-RAND (SC-RAND) EPC, and the University of Ottawa EPC (UO-EPC)—each produced evidence reports. To ensure consistency of approach, the three EPCs collaborated on selected methodological elements, including literature search strategies, rating of evidence, and data table design.
The aim of these reports is to summarize the current evidence concerning the health effects of omega-3 fatty acids on the following: cardiovascular diseases, cancer, child and maternal health, eye health, gastrointestinal/renal diseases, asthma, autoimmune diseases, immune-mediated diseases, transplantation, mental health, and, neurological diseases and conditions. In addition to informing the research community and the public on the effects of omega-3 fatty acids on various health conditions, it is anticipated that the findings of the reports will also be used to help define the agenda for future research.
The focus of this report is on child and maternal health outcomes in humans. In this chapter, the metabolism, physiological functions, and sources of omega-3 fatty acids are briefly discussed. This constitutes background material, putting in context the data presented in the evidence report. As well, the description of the U.S. population intake of omega-3 fatty acids is provided in response to a general question posed within the task order. This introductory material is then complemented by a brief review of the epidemiology and descriptions of the child and maternal health issues related to this intervention. The brief review is intended as an overview, rather than a comprehensive description.
Chapter 2 describes the methods used to identify, review and synthesize the results from studies concerning omega-3 fatty acids and child and maternal health. Chapter 3 presents the findings of studies meeting eligibility criteria, with discussion points, including recommendations for future research completing the report in Chapter 4.
Dietary fat is an important source of energy for biological activities in human beings. It encompasses saturated fatty acids, which are usually solid at room temperature, and unsaturated fatty acids, which are liquid at room temperature. Unsaturated fatty acids can be further divided into monounsaturated and polyunsaturated fatty acids. Polyunsaturated fatty acids (or PUFAs) can be classified, on the basis of their chemical structure, into two groups: omega-3 (n-3) fatty acids and omega-6 (n-6) fatty acids. The omega-3 or n-3 notation means that the first double bond in this family of PUFAs is 3 carbons from the methyl end of the molecule. The same principle applies to the omega-6 or n-6 notation. Despite their differences in structure, all fats contain the same amount of energy (i.e., 9 kcal/g or 37 kJ/g).
Of all fats found in food, two—alpha-linolenic acid (chemical abbreviation: ALA; 18:3 n-3) and linoleic acid (LA; 18:2 n-6)—cannot be synthesized in the human body, yet these are necessary for proper physiological functioning. These two fats are thus called “essential fatty acids.” The essential fatty acids can be converted in the liver to long-chain polyunsaturated fatty acids (LC PUFAs), which have a higher number of carbon atoms and double bonds. These LC PUFAs retain the omega type (n-3 or n-6) of the parent essential fatty acids.
ALA and LA comprise the bulk of the total PUFAs consumed in a typical North American diet. Typically, LA comprises 89% of the total PUFAs consumed, while ALA comprises 9%. Smaller amounts of other PUFAs make up the remainder.1 Both ALA and LA are present in a variety of foods. For example, LA is present in high concentrations in many commonly used oils, including safflower, sunflower, soy, and corn oil. ALA, which is consumed in smaller quantities, is present in leafy green vegetables and in some commonly used oils, including canola and soybean oil. Some novelty oils, such as flaxseed oil, contain relatively high concentrations of ALA, but these oils are not commonly found in the food supply.
The Institute of Medicine (IOM) suggests that, for adults 19 and older, an adequate intake (AI) of ALA is 1.1–1.6 grams/day, and 11–17 grams/day for LA.2 Recommendations regarding AI differ by age and gender groups, and for special conditions such as pregnancy and lactation.
As shown in Figure 1
, eicosapentaenoic acid (EPA; 20:5 n-3) and docosahexaenoic acid (DHA; 22:6 n-3) can act as competitors for the same metabolic pathways as arachidonic acid (AA; 20:4 n-6). In human studies, the analyses of fatty-acid compositions in both blood phospholipids and adipose tissue have shown a similar competitive relationship between omega-3 LC PUFAs and AA. General scientific agreement supports an increased consumption of omega-3 fatty acids and reduced intake of omega-6 fatty acids to promote good health. However, for omega-3 fatty acid intake, the specific quantitative recommendations vary widely among countries not only in terms of different units — ratio, grams, total energy intake — but also in quantity.3
Furthermore, there remain numerous questions relating to the inherent complexities concerning omega-3 and omega-6 fatty acid metabolism, in particular the relationships between the two fatty acids. For example, it remains unclear to what extent ALA is converted to EPA and DHA in humans, and to what extent the high intake of omega-6 fatty acids compromises any benefits of omega-3 fatty acid consumption. Without the resolution of these two fundamental questions, it remains difficult to study the importance of the omega-6/omega-3 fatty acid ratio.
). Once ingested, the parent of the omega-3 fatty acids, ALA, and the parent of the omega-6 fatty acids, LA, can be elongated and desaturated into LC PUFAs. LA is converted into gamma-linolenic acid (GLA; 18:3 n-6), an omega-6 fatty acid that is a positional isomer of ALA. GLA, in turn, can be converted to the long-chain omega-6 fatty acid, AA, while ALA can be converted, to a lesser extent, to the long-chain omega-3 fatty acids, EPA and DHA. However, the conversion from parent fatty acids into LC PUFAs occurs slowly in humans, and conversion rates are not well understood. Because of the slow rate of conversion, and the importance of LC PUFAs to many physiological processes, humans must augment their level of LC PUFAs by consuming foods rich in these important compounds. Meat is the primary food source of AA, and fish is the primary food source of EPA.
The specific biological functions of fatty acids depend on the number and position of double bonds and the length of the acyl chain. Both EPA and AA are 20-carbon fatty acids and are precursors for the formation of prostaglandins (PGs), thromboxane (Tx), and leukotrienes (LTs)—hormone-like agents that are members of a larger family of substances called eicosanoids. Eicosanoids are localized tissue hormones that seem to be one of the fundamental regulatory classes of molecule in most higher forms of life. They do not travel in the blood, but are created in the cells to regulate a large number of processes, including the movement of calcium and other substances into and out of cells, dilation and contraction of muscles, inhibition and promotion of clotting, regulation of secretions including digestive juices and hormones, and, the control of fertility, cell division, and growth.4
, the long-chain omega-6 fatty acid, AA, is the precursor of a group of eicosanoids including series-2 prostaglandins (PG2) and series-4 leukotrienes (LT4). The omega-3 fatty acid, EPA, is the precursor to a group of eicosanoids including series-3 prostaglandins (PG3) and series-5 leukotrienes (LT5). The series-2 prostaglandins and series-4 leukotrienes derived from AA are involved in intense actions (such as accelerating platelet aggregation, and enhancing vasoconstriction and the synthesis of mediators of inflammation) in response to physiological stressors. The series-3 prostaglandins and series-5 leukotrienes derived from EPA are less physiologically potent than those derived from AA. More specifically, the series-3 prostaglandins are formed at a slower rate and work to attenuate excessive series-2 prostaglandins. Thus, adequate production of the series-3 prostaglandins, which are derived from the omega-3 fatty acid, EPA, may protect against heart attack and stroke as well as certain inflammatory diseases like arthritis, lupus, and asthma.4 In addition, animal studies have demonstrated that omega-3 LC PUFAs, such as EPA and DHA, engage in multiple cytoprotective activities that may contribute to antiarrhythmic mechanisms.5 Arrhythmias are thought to contribute to “sudden death” in heart disease.
In addition to affecting eicosanoid production as described above, EPA also affects lipoprotein metabolism and decreases the production of other compounds—including cytokines, interleukin 1β (IL-1β), and tumor necrosis factor α (TNF-α)—which have pro-inflammatory effects. These compounds exert pro-inflammatory cellular actions that include stimulating the production of collagenase and increasing the expression of adhesion molecules necessary for leukocyte extravasation6 The mechanism responsible for the suppression of cytokine production by omega-3 LC PUFAs remains unknown, although suppression of eicosanoid production by omega-3 fatty acids may be involved. EPA can also be converted into the longer chain omega-3 form of docosapentaenoic acid (DPA, 22:5 n-3), and then further elongated and oxygenated into DHA. EPA and DHA are frequently referred to as VLN-3FA—very long chain n-3 fatty acids. DHA, which is thought to be important for brain development and functioning, is present in significant amounts in a variety of food products, including fish, fish liver oils, fish eggs, and organ meats. Similarly, AA can convert into an omega-6 form of DPA.
Studies have reported that omega-3 fatty acids decrease triglycerides (Tg) and very low density lipoprotein (VLDL) in hypertriglyceridemic subjects, concomitant with an increase in high density lipoprotein (HDL). However, they appear to increase or have no effect on low density lipoprotein (LDL). Omega-3 fatty acids apparently lower Tg by inhibiting VLDL and apolipoprotein B-100 synthesis, and decreasing post-prandial lipemia.7 Omega-3 fatty acids, in conjunction with transcription factors (small proteins that bind to the regulatory domains of genes), target the genes governing cellular Tg production and those activating oxidation of excess fatty acids in the liver. Inhibition of fatty acid synthesis and increased fatty acid catabolism reduce the amount of substrate available for Tg production.8
As noted earlier, omega-6 fatty acids are consumed in larger quantities (> 10 times) than omega-3 fatty acids. Maintaining a sufficient intake of omega-3 fatty acids is particularly important since many of the body's physiologic properties depend upon their availability and metabolism.
The major source of omega-3 fatty acids is dietary intake of fish, fish oil, vegetable oils (principally canola and soybean), some nuts such as walnuts, and, dietary supplements. Two population-based surveys, the third National Health and Nutrition Examination (NHANES III) 1988-94, and the Continuing Survey of Food Intakes by Individuals 1994-98 (CSFII), are the main sources of dietary intake data for the U.S. population. NHANES III collected information on the U.S. population aged ≥2 months. Mexican Americans and non-Hispanic African-Americans, children ≤5 years old, and adults ≥ 60 years old were over-sampled to produce more precise estimates for these population groups. There were no imputations for missing 24-hour dietary recall data. A total of 29,105 participants had complete and reliable dietary recall.
The CSFII 1994-96, popularly known as the “What We Eat in America” survey, addressed the requirements of the National Nutrition Monitoring and Related Research Act of 1990 (Public Law 101–445) for continuous monitoring of the dietary status of the American population. The CSFII 1994-96 utilized an improved data-collection method for 24-hour recall known as the multiple-pass approach. Given the large variation in intake from day-to-day, multiple 24-hour recalls are considered to be best suited for most nutrition monitoring and will produce stable estimates of mean nutrient intake from groups of individuals.9 In 1998, the Supplemental Children's Survey, a survey of food and nutrient intake by children under the age of 10 years, was conducted as a supplement to the CSFII 1994-96. The CSFII 1994-96, 1998 surveyed 20,607 people of all ages with over-sampling of low-income population (<130% of the poverty threshold). Dietary intake data from individuals of all ages were collected over 2 nonconsecutive days via two 1-day dietary recalls.
| Grams/day | % Kcal/day | |||
|---|---|---|---|---|
| Mean±SEM | Median (range)1 | Mean±SEM | Median (range)1 | |
| LA (18:2 n-6) | 14.1±0.2 | 9.9 (0 – 168) | 5.79±0.05 | 5.30 (0 – 39.4) |
| ALA (18:3 n-3) | 1.33±0.02 | 0.90 (0 – 17) | 0.55±0.004 | 0.48 (0 – 4.98) |
| EPA (20:5 n-3) | 0.04±0.003 | 0.00 (0 – 4.1) | 0.02±0.001 | 0.00 (0 – 0.61) |
| DHA (22:6 n-3) | 0.07±0.004 | 0.00 (0 – 7.8) | 0.03±0.002 | 0.00 (0 – 2.86) |
The distributions are not adjusted for the over-sampling of Mexican-Americans, non-Hispanic African-Americans, children ≤5 years old, and adults ≥ 60 years old in the NHANES III dataset.
| Grams/day | ||
|---|---|---|
| Mean±SEM | Median±SEM | |
| LA (18:2 n-6) | 13.0±0.1 | 12.0±0.1 |
| Total n-3 FA | 1.40±0.01 | 1.30±0.01 |
| ALA (18:3 n-3) | 1.30±0.01 | 1.21±0.01 |
| EPA (20:5 n-3) | 0.028 | 0.004 |
| DPA (22:5 n-3) | 0.013 | 0.005 |
| DHA (22:6 n-3) | 0.057±0.018 | 0.046±0.013 |
| Food item | EPA | DHA | ALA |
|---|---|---|---|
| Fish (Rawa) | |||
| Anchovy, European | 0.6 | 0.9 | - |
| Bass, Freshwater, Mixed Sp. | 0.2 | 0.4 | 0.1 |
| Bass, Striped | 0.2 | 0.6 | trace |
| Bluefish | 0.2 | 0.5 | - |
| Carp | 0.2 | 0.1 | 0.3 |
| Catfish, Channel | trace | 0.2 | 0.1 |
| Cod, Atlantic | trace | 0.1 | trace |
| Cod, Pacific | trace | 0.1 | trace |
| Eel, Mixed Sp. | trace | trace | 0.4 |
| Flounder & Sole Sp. | trace | 0.1 | trace |
| Grouper, Mixed Sp. | trace | 0.2 | trace |
| Haddock | trace | 0.1 | trace |
| Halibut, Atlantic and Pacific | trace | 0.3 | trace |
| Halibut, Greenland | 0.5 | 0.4 | trace |
| Herring, Atlantic | 0.7 | 0.9 | 0.1 |
| Herring, Pacific | 1.0 | 0.7 | trace |
| Mackerel, Atlantic | 0.9 | 1.4 | 0.2 |
| Mackerel, Pacific and Jack | 0.6 | 0.9 | trace |
| Mullet, Striped | 0.2 | 0.1 | trace |
| Ocean Perch, Atlantic | trace | 0.2 | trace |
| Pike, Northern | trace | trace | trace |
| Pike, Walleye | trace | 0.2 | trace |
| Pollock, Atlantic | trace | 0.4 | - |
| Pompano, Florida | 0.2 | 0.4 | - |
| Roughy, Orange | trace | - | trace |
| Salmon, Atlantic, Farmed | 0.6 | 1.3 | trace |
| Salmon, Atlantic, Wild | 0.3 | 1.1 | 0.3 |
| Salmon, Chinook | 1.0 | 0.9 | trace |
| Salmon, Chinook, Smokedb | 0.2 | 0.3 | - |
| Salmon, Chum | 0.2 | 0.4 | trace |
| Salmon, Coho, Farmed | 0.4 | 0.8 | trace |
| Salmon, Coho, Wild | 0.4 | 0.7 | 0.2 |
| Salmon, Pink | 0.4 | 0.6 | trace |
| Salmon, Pink, Cannedc | 0.9 | 0.8 | trace |
| Salmon, Sockeye | 0.6 | 0.7 | trace |
| Sardine, Atlantic, Canned in Oild | 0.5 | 0.5 | 0.5 |
| Seabass, Mixed Sp. | 0.2 | 0.4 | - |
| Seatrout, Mixed Sp. | 0.2 | 0.2 | trace |
| Shad, American | 1.1 | 1.3 | 0.2 |
| Shark, Mixed Sp. | 0.3 | 0.5 | trace |
| Snapper, Mixed Sp. | trace | 0.3 | trace |
| Swordfish | 0.1 | 0.5 | 0.2 |
| Trout, Mixed Sp. | 0.2 | 0.5 | 0.2 |
| Trout, Rainbow, Farmed | 0.3 | 0.7 | trace |
| Trout, Rainbow, Wild | 0.2 | 0.4 | 0.1 |
| Tuna, Fresh, Bluefin | 0.3 | 0.9 | - |
| Tuna, Fresh, Skipjack | trace | 0.2 | - |
| Tuna, Fresh, Yellowfin | trace | 0.2 | trace |
| Tuna, Light, Canned in Oile | trace | 0.1 | trace |
| Tuna, Light, Canned in Watere | trace | 0.2 | trace |
| Tuna, White, Canned in Oile | trace | 0.2 | 0.2 |
| Tuna, White, Canned in Watere | 0.2 | 0.6 | trace |
| Whitefish, Mixed Sp. | 0.3 | 0.9 | 0.2 |
| Whitefish, Mixed Sp., Smoked | trace | 0.2 | - |
| Wolffish, Atlantic | 0.4 | 0.3 | trace |
| Shellfish (Raw) | |||
| Abalone, Mixed Sp. | trace | - | - |
| Clam, Mixed Sp. | trace | trace | trace |
| Crab, Blue | 0.2 | 0.2 | - |
| Crayfish, Mixed Sp., Farmed | trace | 0.1 | trace |
| Lobster, Northern | - | - | - |
| Mussel, Blue | 0.2 | 0.3 | trace |
| Oyster, Eastern, Farmed | 0.2 | 0.2 | trace |
| Oyster, Eastern, Wild | 0.3 | 0.3 | trace |
| Oyster, Pacific | 0.4 | 0.3 | trace |
| Scallop, Mixed Sp. | trace | 0.1 | - |
| Shrimp, Mixed Sp. | 0.3 | 0.2 | trace |
| Squid, Mixed Sp. | 0.1 | 0.3 | trace |
| Fish Oils | |||
| Cod Liver Oil | 6.9 | 11.0 | 0.9 |
| Herring Oil | 6.3 | 4.2 | 0.8 |
| Menhaden Oil | 13.2 | 8.6 | 1.5 |
| Salmon Oil | 13.0 | 18.2 | 1.1 |
| Sardine Oil | 10.1 | 10.7 | 1.3 |
| Nuts and Seeds | |||
| Butternuts, Dried | - | - | 8.7 |
| Flaxseed | 18.1 | ||
| Walnuts, English | - | - | 9.1 |
| Plant Oils | |||
| Canola (Rapeseed) | - | - | 9.3 |
| Flaxseed Oil | - | - | 53.3 |
| Soybean Lecithin Oil | - | - | 5.1 |
| Soybean Oil | - | - | 6.8 |
| Walnut Oil | - | - | 10.4 |
| Wheatgerm Oil | - | - | 6.9 |
Trace = <0.1;
- = 0 or no data;
Sp. = species;
Except as indicated;
Lox.;
Solids with bone and liquid;
Drained solids with bone;
Drained solids.
The following description is intended only as an overview of the domain of inquiry in which it has been hypothesized that omega-3 fatty acid content, which includes both their intake and their levels in specific biomarkers, plays an important role in maternal pregnancy and child health outcomes in human subjects. This account serves exclusively to introduce the pertinence of this systematic review of the empirical evidence.
Over the past 60 years, the influence of maternal nutrition on fetal growth and development has been extensively studied as part of attempts to understand the causes and consequences of protein-calorie malnutrition.11 This field of investigation has since expanded to encompass experimental, observational and descriptive studies designed to identify the specific roles of a broad range of sources and constituents of maternal nutrition. In addition, studies have also been conducted to evaluate the impact of maternal nutrition on maternal health during pregnancy and pregnancy outcomes. The following overview will focus on the the role played by omega-3 fatty acids in modulating the duration of pregnancy, incidence of pregnancy-induced hypertension, fetal growth and development, and infant (preterm and term) neurocognitive and visual development. The mechanisms by which omega-3 fatty acids or their eicosanoid derivatives impact the observed biological outcomes may include one or more of their identified functions in modulating the cell membrane microenviroment, signaling pathways, and gene expression.12, 13
It has been posited that the accretion of omega-3 fatty acids within, and use by, the maternal biological system has the potential to influence both maternal health during pregnancy, and fetal health. Likewise, it has been hypothesized that their accumulation within, and use by, the post-delivery child's biological system can affect their development and health. However, notwithstanding problems affecting their metabolism or availability, since EFAs must be “obtained” from “external sources” in order for their contents to accumulate and, in turn, potentially influence health, mothers and their fetuses/children require that omega-3 fatty acid content be “delivered” (i.e., via the placenta, breast milk, formula supplementation, food sources such as oily fish, or supplementation).
Birth weight is the single most important factor affecting neonatal morbidity and mortality.14 Infants born with low birth weights (less than 2,500 grams by WHO criterion) may be the result of: 1. being constitutionally small; 2. intrauterine growth retardation (IUGR); or 3. preterm birth. In the United States, approximately 350,000 infants are born weighing less than 2,500 grams.15
Preterm birth is a multifactorial condition that results in significant morbidity and mortality. Premature infants are at risk of injury to every organ system in the newborn period: intraventricular hemorrhage, retinopathy of prematurity, respiratory distress syndrome, chronic lung disease, necrotizing enterocolitis, growth failure, and infections. Of greatest concern for the infants who survive are the risks of developing permanent neurocognitive deficits (i.e., cerebral palsy, hearing and vision loss, cognitive deficits) that impact on their lifelong health and functional capacity.16–19 In addition, studies now suggest that premature infants are at higher risk for developing adult-onset chronic diseases including hypertension, cardiovascular disease, and diabetes, as a result of permanent physiologic changes induced by abnormal conditions during sensitive periods of human growth and development.20–22 There is an hypothesis that suboptimal n-3 and n-6 nutrititure during sensitive periods of fetal growth and development may result in permanent changes in neurocognitive and visual function and the development of adult-onset diseases such as hypertension. In the United States, preterm birth of low birth weight infants is 6%–10% of all births, which is approximately 300,000 annually.23 In the United States, the cost of preterm births is estimated at several billion dollars annually, not including the costs of care for the associated-adult onset diseases.24
Without exploring too deeply what was not, in fact, eligible for synthesis in our review—because it failed to satisfy our eligibility criterion relating to research design—some evidence is introduced here merely to demonstrate that there can coexist more than one interpretation of how maternal intake of omega-3 fatty acids could influence a child outcome. Results of epidemiological studies conducted with residents of the Faroe Islands25, 26 have been taken to suggest that marine diets, which contain omega-3 fatty acids, increase birth weight either by prolonging pregnancy.27 or increasing the fetal growth rate.28, 29 Proposed mechanisms have included: a) the delayed timing of spontaneous delivery, which results from the altered balance among the PGs involved in the initiation of labor;27 or, b) an increased fetal growth rate, which results from enhanced placental blood flow associated with a decreased Tx/prostacyclin ratio28 and decreased blood viscosity.30 These observations might not be replicated in populations that regularly consume lesser amounts of omega-3 fatty acids from marine sources, however. With respect to maternal health during human pregnancy, it has been hypothesized that marine oils may lower risks of certain complications of pregnancy, in particular preterm delivery, intrauterine growth retardation, preeclampsia, and gestational hypertension.31 Given that some of their presumed mechanisms of action overlap with those of aspirin, it was thought that omega-3 fatty acids might protect pregnant women against preeclampsia and gestational hypertension, for example.32–34
Essential fatty acid derived eicosanoids play important roles as biochemical mediators in normal term labor that initiate uterine contractions, cervical maturation, and rupture of membranes.35, 36 There is an elevation of omega-6 fatty acid eicosansoid series (PGE2 and PGF2alpha, LTC4, LTB4) in the maternal circulation prior to the onset of labor37 and inhibition of their synthesis with cyclooxygenase inhibitors stops the onset of labor.38 Women who deliver prematurely have higher erythrocyte total plasma lipid omega-6 fatty acids and lower omega-3 fatty acids compared with women who delivered at term, suggesting that an imbalance in favor of omega-6 fatty acids and their eicosanoid derivatives contribute to the premature onset of labor.39, 40 By altering the balance of omega-6 to omega-3 eicosanoids by diet supplementation with omega-3 fatty acids in human, rodent, and sheep, studies have been successful in increasing the duration of gestation.31, 41–46
In Western societies, placental insufficiency is the major cause of IUGR, with maternal hypertension having the most profound effect.47 Fetal adaptations that are required to compensate for poor placental function result in increased perinatal morbidity and mortality. Of greatest concern is the increased risk for permanent adverse effects on growth and development.47–51 Epidemiologic data suggests that the fetal adaptations may be associated with an increased risk for the development of adult-onset chronic diseases including hypertension, cardiovascular disease, obesity and diabetes.20–22 In keeping with these observations, animals studies on fetal growth restriction demonstrate metabolic, hormonal and end organ changes that predispose the animals to the development of hypertension, cardiovascular disease and diabetes.52–54
Hypertension in pregnancy of varying degrees of severity (chronic hypertension, preeclampsia, eclampsia) occurs in approximately 6%8% of pregnancies and is the second leading cause of maternal death in the United States.55 The pathophysiologic mechanisms of preeclampsia remain unclear but a consistent finding is endothelial dysfunction resulting in intense vasospasm due to increased endothelial sensitivity to pressors.56, 57 It is thought, in part, that the enhanced vasoconstriction may be caused by increased synthesis of the potent omega-6 fatty acid derived vasoconstrictor, thromboxane A2, that is found in maternal plasma and placental tissue of preeclamptic women.58–60 Non-pregnant hypertensive adults have been shown to have significantly lower plasma phospholipids levels of omega-3 fatty acids which results in decreased nitric oxide synthesis and increased aceylcholinesterase activity resulting in increased vascular tone.61, 62 In contrast, populations with high marine oil intake or hypertensive patients supplemented with omega-3 fatty acids had higher plasma omega-3 fatty acid levels had lower blood pressures.62–66 Inuit women who ate a diet rich in marine foods were 2.6 times less likely to develop hypertension during pregnancy than Inuit women whose diets contained less marine foods.67 Supplementation with omega-3 fatty acids would correct an imbalance between prostacylin and thromboxane, reduce blood viscosity, reduce endogenous pressors, or alter baroreceptor function which may help to reduce the occurrence of hypertension in pregnancy.68–73
Normal placental blood flow is critical for adequate delivery of nutrients to the fetus to support normal growth and development. It has been proposed that the balance of omega-3 and omega-6 derived eicosanoids may play a key role in maintaining adequate placental blood flow and delivery of nutrient substrates to support normal fetal growth and development.74, 75 Based on biochemical indices (decreased PGI2 synthesis and increased 20:5n-6 DPA content of umbilical artery endothelium), it appears that low birth weight infants are deficient in omega-3 fatty acids.74 In addition, observational and interventional studies have demonstrated a direct association between fetal growth and maternal intake of omega-3 fatty acids.24, 74–77
In keeping with other nutrients, the bulk of fatty acid delivery and storage in the fetus occurs in the last trimester. Infants born prematurely have lower total body content of omega-3 LCPUFA.78–80 Omega-3 fatty acids accumulate in fetal fat stores, liver and neural tissues. The highest quantities are found in fat stores, but the relative proportion of omega-3 LCPUFA is highest in the retina and brain.79 It appears that the fetus is dependent on the maternal supply of omega-3 LCPUFA with levels in the umbilical plasma phosphoplipids that strongly correlate with maternal plasma phospholipids.81–84
The fetus is capable of converting ALA (18:3n-3) to DHA, but it remains controversial as to whether the rate of conversion is adequate to meet their needs.85–87 Preformed DHA is preferentially transferred from the maternal circulation to the fetus, although the mechanism is unclear.74, 88, 89 Maternal stores of DHA are mobilized during pregnancy for transfer to the fetus since plasma DHA (g/ml or FA%) has been shown to be decreased in multiparous versus primiparous women. This finding correlated with the lower DHA FA% in cord tissue of higher birth order newborns. Taken together, these findings suggest that the current omega-3 fatty acid intake during pregnancy in Western countries is inadequate.90
Parallel to the high rates of fatty acid delivery and accretion in the fetus in the third trimester, is the rapid growth and development of neural tissues which continues for the first 18 months after birth.81, 91 During this period, the accretion of DHA in the brain is about 3 times greater than the relative increase in brain weight.92 DHA accretion in the human retinal begins in the third trimester and peaks at 36–40 weeks gestation.93 DHA and AA have been identified as important structural components of the highly specialized membrane lipids of the human central nervous system, with phospholipids of brain gray matter containing high proportions of DHA.94–96 DHA has also been observed to be the major LCPUFA in the outer segments of the retina's rods and cones.94 The functional roles of DHA were first shown in animals (fetus or newborn) deprived of DHA. Investigators have reported that the depletion of DHA from the developing retina and brain leads to abnormal electroretinograms (ERGs) and decreased VEP responses, in addition to altered learning behavior (e.g., performance in maze tasks, habituation, exploratory activity in novel environments, brightness discrimination, and olfactory-based learning tasks).97–104 There is concern with findings that suggest that these changes in function may be irreversible despite correction of DHA status after deprivation of omega-3 fatty acids during critical periods of retinal development.105 As well, the dietary deficiency of ALA in developing animals has resulted in decreased DHA levels, with a reciprocal increase in omega-6 fatty acids, and especially DPA, observed in the retina, whole brain, isolated brain membranes, and specific brain regions.106–108
Animal studies have suggested the value of providing omega-3 fatty acid supplementation as well. Recent studies have shown that omega-3 fatty acids alter the metabolism of dopamine and serotonin in the brain of rodents and piglets.109–114 Particular interest has been given to the dopaminergic system because of its role in the cognitive advances of early childhood, for example, as a modulator of attention and motivation, and in the visual pathways.115 Other recent studies have suggested that omega-3 fatty acids regulate the expression of genes involved in cytoskeleton and membrane association, signal transduction, ion channel formation, energy metabolism, synaptic plasticity, and the retinoid X receptor in the brain.116–119
Supplementation with DHA in human infants have shown variable results, with improved visual acuity demonstrated in premature infants120–123 and variable results in term infants.124–127 In part, the variability was thought to be due to differences in study design, age and duration of intervention, method(s) of assessment. The different measures of visual function may reflect different neural processes, making the comparison of findings between studies problematic. For example, the Teller acuity card or forced choice preferential looking method evaluates an infant's tendency to gaze at a pattern and assesses not only visual acuity but also an infant's ability to respond which requires integration of motor and behavioral responses to the visual stimuli. Visual evoked potentials (VEP) directly measures the amplitude of electrical responses to visual stimuli that signal transduction from the eye to visual cortex and is not dependent on the infant's behavioral state or motor abilities.
Based on observational studies, it has been shown that human milk fed infants have improved neurocognitive development compared to formula fed infants, it was hypothesized that one of the contributing factors may be the availability of long chain derivatives of LA and ALA that is present only human milk82, 128 This difference in fatty acid intake is reflected in lower erythrocyte membrane phospholipid DHA in infants fed formula.82 Until the recent availability infant formula with added omega-3 LCPUFA, standard infant formula was devoid of these fatty acids. Human milk contains DHA ranging from 0.2 to 0.4 FA% and varies considerably among different populations with differences in DHA intake.120, 124 It is thought that the rate of conversion of ALA (18:3n-3) present in standard infant formula to DHA does not meet rates of accretion in the CNS that is seen in human milk fed infants.129–131 As with the DHA intervention trials in term infants on visual acuity, the effect of DHA supplementation on neurocognitive development is also inconsistent.127, 132–134 Thevariability may, in part, be due to the use of different assessment tools.
While it could be hypothesized that the intake of omega-3 fatty acids might have a greater impact on preterm, than term, infants because the former have been exposed for a shorter period of time to what the latter likely received as significant contributors to their development, the present review was not planned to test this hypothesis. Even so, there may be considerable justification for giving omega-3 fatty acids to mothers who eventually deliver term babies as well as to these term infants post-delivery. Mothers of term infants may not exhibit uniform levels of omega-3 fatty acid content in their biomarkers, which are passed on to their children.
For example, it has recently been observed that the human milk of North American women has significantly less DHA and AA content, when compared with milk obtained from women in China, Japan, or India.135, 136 Furthermore, higher amounts of DHA in human milk have been associated with higher plasma and erythrocyte levels of DHA in breastfed infants;137–139 and, a significant association between DHA levels in human milk and visual evoked potential (VEP) acuity was recently reported in a cross-sectional study of breastfed infants in Denmark.140 Related observations, which are reviewed in depth here, suggest the possible importance of the intake of omega-3 fatty acids by pregnant and lactating women for the health of their offspring.
Moreover, when compared with women with lower plasma levels of AA and DHA during gestation, women with higher plasma levels gave birth to infants with higher levels of AA and DHA;137, 141, 142 and, higher levels of omega-6 and omega-3 fatty acid content in biomarkers at birth were found to be associated with higher blood levels of AA and DHA in the infant for several weeks after birth.138, 140, 143 Thus, individual differences in the levels of fatty acid content observed in mothers' biomarkers, which appear to be paralleled by individual differences in the levels of fatty acid content in the biomarkers obtained from their children, might ultimately be found to account for differences in child development. DHA deficiency related to low maternal intake of omega-3 fatty acids during pregnancy, for example, might adversely impact child development.
Direct measurement of tissue levels is not feasible for most tissues such as brain and retina. As such, fatty acid biomarkers are used as surrogate measures of tissue levels. How closely these biomarkers reflect tissue levels are not certain.131, 144–147 Different measurements of the fatty acid content of different lipid pools reflect either the effects of short term (hours) or long term (days to months) dietary intake of fatty acids.
The likely significance of omega-3 fatty acids for child health is therefore suggested by the observations that: a) the human brain and retina each contain considerable omega-3 fatty acid content; b) the child delivered at term receives an important supply of omega-3 fatty acids especially in the third trimester of pregnancy; and, c) due to a shortened gestational period, the child delivered prematurely receives less exposure to omega-3 fatty acid content than does the term child. Not surprisingly, the observation concerning preterm infants has afforded considerable empirical study of the impact of omega-3 fatty acids on their health. This evidence is systematically reviewed here.
Given this overview, and the expected availability of empirical evidence, we aimed to evaluate the impact of omega-3 fatty acid content (i.e., intake; in biomarkers), from any and all sources (e.g., breast milk; formula), on the growth patterns, neurological development, visual development, and cognitive development of preterm and term children. We also planned to investigate the influence of omega-3 fatty acid content (i.e., intake; in biomarkers), from any and all sources (e.g., food; supplements), on specific pregnancy outcomes relating to offspring (i.e., preterm births; children born small for gestational age) and maternal health (i.e., preeclampsia; eclampsia; gestational hypertension). However, as pointed out in Chapter 2, not all of the relationships between the intake of omega-3 fatty acids, the fatty acid content of biomarkers, and clinical-developmental outcomes are investigated in either population (i.e., maternal; child).
It should also be pointed out that, given the likely important role played by the omega-6 fatty acids—and AA in particular—in health and development, their co-influence on clinical and developmental outcomes are investigated, where possible. Finally, safety data (i.e., adverse effects) are evaluated. For example, concerns have been raised about the safety of fish oil supplementation in infants and pregnant women include, decreased platelet aggregation, immunosuppression, growth148, 149 and environmental contaminants.26, 132, 148–151 However, the clinical significance of these potential risks need to be determined.
The UO-EPC's evidence report on omega-3 fatty acids in child and maternal health is based on a systematic review of the scientific-medical literature to identify, and synthesize the results from, studies addressing key questions. Together with content experts, UO-EPC staff identified specific issues integral to the review. A Technical Expert Panel (TEP) helped refine the research questions as well as highlighted key variables requiring consideration in the evidence synthesis. Evidence tables presenting key study-related characteristics were developed and are found in the Appendices. In-text summary tables were derived from the evidence tables. The methodological quality and generalizability of the included studies was appraised, and individual study results were summarized.
The purpose of this evidence report was to synthesize information from relevant studies to address various questions. The questions are organized by the type of population (i.e., maternal/pregnancy versus child [e.g., term versus preterm delivery]) and the type of outcome data (i.e., clinical/pregnancy versus clinical/child-developmental capacity versus biological/biomarker status versus adverse effects):
Maternal population, clinical/pregnancy outcomes:
What is the evidence that intake of omega-3 fatty acids influences the duration of gestation in women with or without a history of a previous preterm birth (gestational duration less than 37 weeks)?
What is the evidence that maternal intake of omega-3 fatty acids influences the incidence of preeclampsia, eclampsia or gestational hypertension?
What is the evidence that maternal intake of omega-3 fatty acids influences the incidence of births of human infants small for gestational age?
Maternal population, biomarker data relating to clinical/pregnancy outcomes:
What is the evidence that the duration of gestation in women with or without a history of a previous preterm birth is associated with the omega-3 or omega-6/omega-3 fatty acid content of maternal biomarkers during pregnancy?
What is the evidence that the incidence of preeclampsia, eclampsia or gestational hypertension is associated with the omega-3 or omega-6/omega-3 fatty acid content of maternal biomarkers during pregnancy?
What is the evidence that the incidence of births of human infants small for gestational age is associated with the omega-3 or omega-6/omega-3 fatty acid content of maternal biomarkers during pregnancy?
Child population, growth pattern outcomes:
What is the evidence that maternal intake of omega-3 fatty acids during pregnancy influences growth patterns in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of maternal breast milk, with or without known maternal intake of omega-3 fatty acids, influences growth patterns in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of infant formula influences growth patterns in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of maternal breast milk, with or without known maternal intake of omega-3 fatty acids, and together with the omega-3 fatty acid content of infant formula, influences growth patterns in term or preterm human infants?
What is the evidence that intake of omega-3 fatty acids from sources other than maternal breast milk or infant formula supplemented with omega-3 fatty acids, by term or preterm human infants, influences growth patterns?
Child population, biomarker data relating to growth pattern outcomes:
What is the evidence that term or preterm human infants' growth patterns are associated with the omega-3 or omega-6/omega-3 fatty acid content of maternal biomarkers during pregnancy?
What is the evidence that term or preterm human infants' growth patterns are associated with the omega-3 or omega-6/omega-3 fatty acid content of fetal biomarkers during pregnancy?
What is the evidence that term or preterm human infants' growth patterns are associated with the omega-3 or omega-6/omega-3 fatty acid content of child biomarkers?
Child population, neurological development outcomes:
What is the evidence that maternal intake of omega-3 fatty acids during pregnancy influences neurological development in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of maternal breast milk, with or without known maternal intake of omega-3 fatty acids, influences neurological development in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of infant formula influences neurological development in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of maternal breast milk, with or without known maternal intake of omega-3 fatty acids, and together with the omega-3 fatty acid content of infant formula, influences neurological development in term or preterm human infants?
What is the evidence that intake of omega-3 fatty acids from sources other than maternal breast milk or infant formula supplemented with omega-3 fatty acids, by term or preterm human infants, influences neurological development?
Child population, biomarker data relating to neurological development outcomes:
What is the evidence that term or preterm human infants' neurological development is associated with the omega-3 or omega-6/omega-3 fatty acid content of maternal biomarkers during pregnancy?
What is the evidence that term or preterm human infants' neurological development is associated with the omega-3 or omega-6/omega-3 fatty acid content of fetal biomarkers?
What is the evidence that term or preterm human infants' neurological development is associated with the omega-3 or omega-6/omega-3 fatty acid content of child biomarkers?
Child population, visual function outcomes:
What is the evidence that maternal intake of omega-3 fatty acids during pregnancy influences visual function in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of maternal breast milk, with or without known maternal intake of omega-3 fatty acids, influences visual function in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of infant formula influences visual function in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of maternal breast milk, with or without known maternal intake of omega-3 fatty acids, and together with the omega-3 fatty acid content of infant formula, influences visual function in term or preterm human infants?
What is the evidence that intake of omega-3 fatty acids from sources other than maternal breast milk or infant formula supplemented with omega-3 fatty acids, by term or preterm human infants, influences visual function?
Child population, biomarker data relating to visual function outcomes:
What is the evidence that term or preterm human infants' visual function is associated with the omega-3 or omega-6/omega-3 fatty acid content of maternal biomarkers during pregnancy?
What is the evidence that term or preterm human infants' visual function is associated with the omega-3 or omega-6/omega-3 fatty acid content of fetal biomarkers?
What is the evidence that term or preterm human infants' visual function is associated with the omega-3 or omega-6/omega-3 fatty acid content of child biomarkers?
Child population, cognitive development outcomes:
What is the evidence that maternal intake of omega-3 fatty acids during pregnancy influences cognitive development in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of maternal breast milk, with or without known maternal intake of omega-3 fatty acids, influences cognitive development in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of infant formula influences cognitive development in term or preterm human infants?
What is the evidence that the omega-3 fatty acid content of maternal breast milk, with or without known maternal intake of omega-3 fatty acids, and together with the omega-3 fatty acid content of infant formula, influences cognitive development in term or preterm human infants?
What is the evidence that intake of omega-3 fatty acids from sources other than maternal breast milk or infant formula supplemented with omega-3 fatty acids, by term or preterm human infants, influences cognitive development?
Child population, biomarker data relating to cognitive development outcomes:
What is the evidence that term or preterm human infants' cognitive development is associated with the omega-3 or omega-6/omega-3 fatty acid content of maternal biomarkers during pregnancy?
What is the evidence that term or preterm human infants' cognitive development is associated with the omega-3 or omega-6/omega-3 fatty acid content of fetal biomarkers?
What is the evidence that term or preterm human infants' cognitive development is associated with the omega-3 or omega-6/omega-3 fatty acid content of child biomarkers?
Maternal or child population, adverse effects:
What is the evidence for the risk, in pregnant women, of short and long-term adverse events related to their intake of omega-3 fatty acids?
What is the evidence for the risk, in breastfeeding women, of short and long-term adverse events related to their intake of omega-3 fatty acids?
What is the evidence for the risk, in term or preterm human infants, of short and long-term adverse events related to maternal intake of omega-3 fatty acids during pregnancy?
What is the evidence for the risk, in term or preterm human infants, of short and long-term adverse events related to their intake of omega-3 fatty acids after birth (e.g., maternal breast milk, infant formula supplemented with omega-3 fatty acids)?
What is the evidence that these adverse events, or any contraindications, are associated with the intake of specific sources (e.g., marine, plant), types (e.g., EPA, DHA, ALA) or doses of omega-3 fatty acids, including in specific populations such as diabetics?
The overarching goal was to identify and systematically review whatever evidence exists within the eligibility boundaries established for this review in consultation with our TEP and in light of the topics being addressed by SC-RAND and Tufts-NEMC EPCs. These boundaries are delineated in the Eligibility Criteria section (below). At all times, data obtained from children delivered at term and preterm (i.e., gestational duration less than 37 weeks) were evaluated separately. More details concerning the questions are provided in conjunction with the description of the Analytic Frameworks (below).
We were also guided collectively by ODS, our TEP and our UO-EPC review team content experts to examine, where data permitted, the possible influence on efficacy, association or safety evidence of the following potential effect modifiers:
intervention/exposure length;
timing of intervention/exposure period (e.g., beginning the 3rdday of life, for 4 months);
type(s) of omega-3 fatty acid (e.g., ALA, EPA, DHA);
source of the omega-3 fatty acids (e.g., marine, plant, nut), including the specific source (e.g., mackerel as an oily fish);
total caloric/energy intake;
delivery format (e.g., whole food servings, capsules, pourable or spreadable oils);
dose/serving size, including the precision/control of its delivery (e.g., per-day specific, minimum, maximum or range of numbers of capsules, whole food servings or bottle-pourable litres);
type of processing used to purify the intervention/exposure and/or to maintain the experimental blind (e.g., ethyl esterification; adding an anti-oxidant to stabilize/preserve oils; adding flavor to oils; [vacuum] deodorization);
amount/dose of omega-6 fatty acid intake either added as a cointervention or identified as being present in the background diet, thereby establishing a specific, minimum, maximum or range of allowable or mandated on-study omega-6/omega-3 fatty acid intake;
the identity of the manufacturer and/or certain characteristics of their product(s) (i.e., purity; presence of other potentially active agents that have not been added intentionally: e.g., methylmercury content);
for questions relating to efficacy or association, the prestudy/baseline or on-study omega-3 or omega-6/omega-3 fatty acid content of blood lipid biomarkers;
absolute or relative omega-3 fatty acid content of the prestudy/baseline diet;
omega-6/omega-3 fatty acid content in the prestudy/baseline diet, with the study population's country of origin as a possible surrogate measure of the omega-6/omega-3 fatty acid content of the background diet; and,
any study subpopulations (e.g., minority; ethnic; genetic, including diabetics).
Furthermore, where data permitted, the following factors with the potential to influence child and maternal health outcomes were also investigated:
obstetric history (e.g., maternal age at conception and delivery; history of a previous and/or current preterm birth [length in weeks; etiology; spontaneous versus induced; history of preeclampsia, eclampsia or gestational hypertension; history of a previous birth of an infant small for gestational age);
gynecologic history (e.g., uterine abnormalities);
maternal general health history (e.g., medical and psychiatric), including maternal medication/treatment history (e.g., prescription and non-prescription drugs);
breastfeeding history;
setting (e.g., tertiary care hospital; community facility);
other sociodemographic/economic factors (e.g., marital status, education, income, employment status);
other maternal cointerventions (e.g., other supplement use [e.g., vitamins, minerals], psychological interventions, use of complementary/alternative [CAM] medicine/products);
maternal illicit drug use history;
history of domestic violence;
maternal smoker history;
history of maternal alcohol consumption;
prenatal history (e.g., delivery anomalies);
neonatal history (e.g., asphyxia; intracranial hemorrhage);
pediatric history (e.g., medications/treatments; supplement use [e.g., vitamins, minerals]; immunizations); and,
with respect to each child outcome in turn (e.g., cognitive development), the developmental capacity/status regarding the other child outcomes (i.e., growth patterns [e.g., weight, height and head circumference at birth]; neurological development; visual development).
Parental smoking and alcohol consumption especially during pregnancy yet also post-delivery are particularly important effect modifiers in that they have been observed to influence both child or maternal health and essential fatty acid status, with levels of the latter potentially affecting the former.152
Populations of interest in rectangles. Exposure in oval. Outcomes in rounded rectangles. Effect modifiers in hexagons. Solid connecting arrows indicate associations and effects reviewed in this report.
Populations of interest in rectangles. Exposure in oval. Outcomes in rounded rectangles. Effect modifiers in hexagons. Solid connecting arrows indicate associations and effects reviewed in this report.
) highlights maternal outcomes, whereas a second one focuses on child/developmental capacity outcomes (Figure 3). The possibility of adverse events (e.g., side effects) and contraindications is recognized in each framework. In short, the analytic frameworks outline the various lines of logic defining the review's research questions. But, not all linkages in each analytic framework were investigated.
) or developmental (i.e., child population: Figure 3) outcome. Likewise, to be eligible for inclusion in the review each study had to entail an investigation of at least one such outcome. Considering the purpose of the two-year task order is to afford a clinically-relevant research agenda, this decision was judged to be appropriate by both our TEP and our review team. Thus, excluded were studies whose sole focus was to examine the impact of omega-3 fatty acid interventions or exposures on the omega-3 or omega-6/omega-3 fatty acid content of biomarkers, even if the study populations met other eligibility criteria for the present review.
).
The clinical events constitute the outcomes of interest, and include the shorter-than-term duration of gestation, the birth of an infant small for gestational age, or the maternal development of preeclampsia, eclampsia, or gestational hypertension. Otherwise “healthy” pregnant women, with or without a history of the following, constitute the study populations of interest:
a previous preterm birth (i.e., gestational duration less than 37 weeks);
preeclampsia, eclampsia or gestational hypertension; or,
a previous birth of an infant small for gestational age.
).
At the time they and their breast milk serve as the child's source of omega-3 fatty acids, mothers may or may not have been receiving a supply of omega-3 fatty acids in their diet and/or from supplementation. The developmental arcs constitute the clinical-developmental outcomes of interest: growth patterns, neurological development, visual development, and cognitive development. The child populations of interest include otherwise “healthy” children delivered at term or preterm, with data from these populations investigated separately.
Overall, questions pertaining to maternal populations center on the possible preventive, or protective, value of omega-3 fatty acid content (i.e., intake and/or in biomarkers) with respect to specific pregnancy outcomes. On the other hand, questions regarding child populations concern the possible value of omega-3 fatty acid content (i.e., intake and/or in biomarkers) in facilitating (e.g., “catching up to,” maintaining, or accelerating) expected or possible types or rates of development. Questions relating to adverse effects in both populations are investigated with data obtained from interventional/exposure studies meeting eligibility criteria.
The possible influence of predefined effect modifiers is evaluated in relation to each of the questions. Where data permit, question-specific sections titled “Impact of Covariates and Confounders” elucidate a) those variables (e.g., intervention/exposure; population) that were consistently observed, across reviewed studies, to influence study outcomes as well as b) those variables (e.g., caloric/energy intake; smoker status; alcohol consumption), which having been controlled for either experimentally or analytically in reviewed studies, were observed to consistently influence, or consistently fail to influence, study outcomes.
The search strategy for this project was designed to be comprehensive and achieve the highest possible recall of relevant clinical studies. The electronic search strategy was developed by an information specialist in consultation with clinical content experts in child and maternal health. The child and maternal health search concept was combined with the core omega-3 fatty acids search strategy established in collaboration with the project librarians, biochemists, nutritionists, and clinicians from the three EPCs involved in the 2-year, Health Benefits of Omega-3 Fatty Acids task order. Consultation among these sources provided the biochemical names and abbreviations of omega-3 fatty acids, names of commercial omega-3 fatty acids products, and food sources of omega-3 fatty acids.
The following electronic databases were searched: Medline (1966 - November Week 2 2003 and updated to February Week 3 2004), Premedline (Dec 13 2003), Embase (1980 to 2003 Week 50 and updated to 2004 Week 09), the Cochrane Library including the Cochrane Central Register of Controlled Trials (3rd Quarter 2003) and CAB Health (1973-Sept 2003). All databases were searched via the Ovid interface using Search Strategy 1 (Appendix A *), except CAB Health, which was searched through SilverPlatter using Search Strategy 2 (Appendix A). Searches were not restricted by language of publication, publication type, or study design, except with respect to the MeSH term “dietary fats,” which was limited by study design to increase its specificity. A total of 2,932 bibliographic records were downloaded, with duplicate records identified and removed using citation management software (Reference Manager®).
Reference lists of included studies, book chapters, and narrative or systematic reviews retrieved after having passed the first level of relevance screening, were manually searched to identify additional unique references. Through contact with content experts, attempts were made to identify both published and unpublished studies. On behalf of the three EPCs investigating the evidence concerning the health benefits of omega-3 fatty acids, a letter was written to industry representatives to obtain additional evidence (Appendix B *). Investigators who frequently published study reports that were included in the review were contacted to clarify which of their reports were companion documents (i.e., multiple reports referring to the same study yet where each contains some unique outcome data or unique descriptions of the methods: e.g., additional follow-up data) or duplicate documents (i.e., a report which exclusively presents data published elsewhere). These informants were also asked to provide citations or copies of reports that our searches failed to detect and to identify the study each described. Investigators who responded with clarifying information included: Drs. Eileen Birch, Susan Carlson, Maria Makrides, Sjurdur Frodi Olsen, and Mary Fewtrell. All of these supplementary efforts to identify more evidence identified an additional 18 records that were entered into the collection for review. A final set of 2,049 unique references was identified.
Published and unpublished studies, written in any language, were eligible for inclusion. Excluding grey literature from systematic reviews of interventions can lead to the overestimation of effect sizes.153 Substantial bias in the results of a systematic review pertaining to a complementary/alternative medical (CAM) intervention can ensue from the exclusion of data from reports written in languages other than English.154 AHRQ and ODS consider omega-3 fatty acids to be a CAM exposure.
To maximize their generalizability, clinical, developmental and biomarker data were required from live, otherwise “healthy” human study populations or subpopulations (e.g., genetic, minority, ethnic: e.g., diabetic) of any age. For sake of simplicity, we decided to use the generic term “child” when referring to infants (less than 12 months of age), toddlers and children up to 18 years old. Excluded were studies whose biomarker data were solely obtained from aborted fetuses because the circumstances associated with or leading to spontaneous or elective abortions (e.g., chromosomal abnormalities; non-chromosomal congenital abnormalities) could influence the fatty acid status of biomarkers in ways that would preclude an interpretation of these observations that is meaningful for the purposes of the present review. Moreover, different types of abnormal fetus may exhibit different rates of omega-3 fatty acid accumulation in tissue and/or different patterns of tissue-specific omega-3 fatty acid accumulation during gestation, resulting in the limited generalizability of the respective data.
Explicit affirmation of the health status of both the maternal and child populations, as well as the preterm/term status of the child populations, had to be provided in study reports. The concept of “child” was not predefined, and the impact on outcomes of any idiosyncratic definitions could not be evaluated post hoc. To allow the meaningful comparison of results from term and preterm infants, age was defined as postconceptional age. Also, if a study did not distinguish data obtained from term and preterm births, it was excluded from the review. Additional details concerning eligibility criteria (e.g., specific types of population required to address the research questions) have already been described with reference to the Analytic Frameworks, and are not repeated here. Excluded populations were those with peroxisomal (e.g., Zellweger's) disorders since this topic was addressed in SC-RAND's year-2 review of the evidence concerning omega-3 fatty acids in neurology.
Ideal interventional/exposure studies of newborns might be expected to enroll and expose them to sources of omega-3 fatty acids immediately post-delivery so as to have, at least in theory, the greatest possible impact on development, and to minimize confounding from earlier exposure to other sources of nutrition,. However, neither the exact or requisite timing of the onset of the intervention/exposure nor the absence of an intervention/exposure to other sources of nutrition (e.g., parenteral feeding in preterm infants) prior to study entry constituted eligibility criteria. Plans were nevertheless made to explore, where data would permit, the possible impact of these factors on outcomes.
No restrictions on the length or number of followups with respect to either study population were pre-established. Yet, given the dynamic nature of development, ideal studies of children might be thought to include multiple followups conducted at least according to expected developmental milestones specific to the four types of developmental arc of interest to the present review.
Interventional/exposure studies had to specifically investigate foods or supplements known to contain omega-3 fatty acids of any type (e.g., EPA, ALA), from any source (e.g., mother's milk, fish, walnuts, seed oil), any serving size or dose, delivered in any fashion (e.g., breastfeeding, capsules, liquid, LCPUFA-rich diet), and for any length of time. In all studies, some method had to have been employed to suggest the presence of omega-3 fatty acid content in the exposure, if not its actual amount (e.g., g/d). Studies investigating “PUFAs” or “ LC PUFAs,” or even types of diet one might presume would contain marine or land sources of omega-3 fatty acids (e.g., “Mediterranean diet”) at minimum had to highlight at least one source of the omega-3 fatty acid content (e.g., oily fish servings). No restrictions were placed on the types or doses of pre- or on-study cointerventions (e.g., omega-6 fatty acid intake, other dietary supplements). While omega-6 fatty acids appear to play a key role in health and development, and their possible co-influence on outcomes is thus assessed in our review, studies exclusively investigating their impact on health outcomes are excluded. A table placed at the end of this report summarizes the content of the fatty acids (and other constituents) in the various types of infant formula provided as supplementation in the included studies.
Randomized controlled trials (RCTs) are the gold standard method to investigate questions of intervention efficacy or effectiveness.155 and were sought to address the research questions. If at least two RCTs were identified, no other types of design were required. Yet, if insufficient numbers of RCT were retrieved, non-RCT (i.e., controlled clinical trials, without random allocation) and observational studies were included. Excluded from this review were descriptive study designs, however (i.e., noncomparative case series; case studies).
RCTs exhibit a greater inherent potential to deal with potentially serious biasing influences (e.g., selection bias) although a poorly designed or conducted RCT can produce results whose interpretability is no less complicated by the presence of confounding influences, for example, than observations derived from a well-constructed and conducted study employing a design with a lesser intrinsic capacity to control for these biases (e.g., non-RCT; prospective cohort study). For example, not all intervention RCTs succeed, either through an explicit experimental plan or the process of randomization per se, to equally distribute known confounding influences (e.g., background diet; energy/caloric intake from the intervention) across their respective study groups.
That said, questions concerning the impact on child developmental outcomes of omega-3 fatty acid intake via formula supplementational alone, or formula supplementation given in addition to breast milk, could be investigated exclusively by RCT evidence. Other questions required the inclusion of observational study evidence (e.g., maternal intake of omega-3 fatty acids, and child developmental outcomes; the role of biomarkers). The observational studies included cross-sectional designs, which by virtue of the lack of temporal separation in their assessments of exposure and outcome, constitute the weakest evidence when it comes to suggesting causal relationships.
Any definition of control or comparator was permitted in the controlled studies (e.g., DHA versus olive oil placebo). However, not every control or comparator group constituted the most appropriate one. For example, with women in a study permitted to choose either to breast- or formula-feed their child, selection bias makes the analyzed comparison of the outcomes from these two groups difficult to interpret unequivocally. The breatfeeding group cannot be construed as the most appropriate control, even though some manufacturers of formula supplementation have attempted to match their fatty acid contents and other constituents to what is contained in human breast milk.
Designs potentially affording less equivocal interpretations include women, having chosen not to breastfeed their children, being randomized to receive formula supplementation either with or without omega-3 fatty acid content. These data would be eligible for inclusion in one type of meta-analysis in our review. Often, as stated earlier, these designs can also include women who exclusively chose to breastfeed their children. However, data from the breastfed children in such studies are exclusively used here as a possible reference standard, or comparison group, yet whose data are not entered into possible meta-analysis as control observations. Another type of design potentially affording less equivocal interpretations involve women, having chosen to exclusively breastfeed their children, who are then randomized to receive formula supplementation either with or without omega-3 fatty acid content. These data would be eligible for an independent meta-analysis.
The specific pregnancy outcomes were identified with reference to the Analytic Frameworks. Any and all child developmental outcomes reflecting the four categories of developmental arc were considered relevant. As markers of omega-3 fatty acid metabolism, the following fatty acid compositions or concentrations, from any source (e.g., red blood cell [RBC] membranes, plasma phospholipids), were considered relevant: EPA, DHA, AA/EPA, AA/DHA, AA/EPA+DHA. Studies exclusively evaluating the role of other biomarkers (e.g., cytokine production, eicosanoid levels), including preconditions (e.g., specific PG levels) often thought to be associated with our review-relevant clinical outcomes (i.e., the development of preeclampsia), were not included. These decisions were made with the assistance of our TEP.
The present review employed specific electronic functionality in the form of an internet-based software system, housed on a secure web site. It brings appreciable efficiencies to the systematic review process and the management of a systematic review team. Electronic yields of literature searches are posted to the system for review. Reviewers then submit all of their results of relevance screening, data appraisal or data abstraction directly to the system. The software system automatically conducts an internal comparison of multiple reviewers' responses to screening questions, to determine the eligibility/relevance of a bibliographic record or a full report. As well, the software captures responses to specific requests to abstract pre-specified data (e.g., mean age of study participants; the assessment of a study's internal validity) from pertinent reports. One large advantage associated with using this software is that review team members are able to complete their work from wherever they have internet access.
Following a calibration exercise, which involved screening five sample records using an electronic form developed and tested especially for this review (Appendix C *), two reviewers independently screened the title, abstract, and key words from each bibliographic record for relevance by liberally applying the eligibility criteria. A record was retained if it appeared to contain pertinent study information. If the reviewers did not agree in finding at least one unequivocal reason for excluding it, it was entered into the next phase of the review. The reasons for exclusion were noted using a modified QUOROM format (Appendix D).156 The screening process also aimed to identify the exact child and maternal health question a record addressed, in addition to determining whether it might also or instead pertain to any of the other topics being systematically reviewed by the three EPCs in year 2 of the omega-3 fatty acids project.
Print or electronic copies of the full reports for those citations having passed level one screening were then retrieved. After completing a calibration exercise which involved evaluating five sample reports using the same eligibility criteria (Appendix C), the rest of the reports were independently assessed by two reviewers. Reports were not masked given the equivocal evidence regarding the benefits of this practice.157 To be considered relevant at this second level of screening, all eligibility criteria had to be met. A third level of dual-review screening aimed to exclude studies whose designs were not required to investigate the research questions (see Eligibility Criteria). All the levels of evidence were reviewed and when there were at least one study to address a given question, it was included regardless of the level of evidence. However, if there were at least two RCTs addressing the question, lower level of evidence reports were excluded (see list of excluded observational trials in Appendix F).
Disagreements arising either at screening levels 2 or 3 were resolved by consensus and, if necessary, third party intervention. Excluded studies at each of these levels are noted as to the reason for their ineligibility in listings found at the end of this report.
Following a calibration exercise involving two studies, 11 reviewers independently abstracted the contents of included studies using an electronic Data Abstraction form developed especially for this review (Appendix C *). A second reviewer then verified these data. Data abstracted included the characteristics of the:
report (e.g., publication status, language of publication, year of publication);
study (e.g., sample size; research design; number of study arms/groups, cohorts, or phases; funding source);
population (e.g., preterm versus term status);
intervention/exposure (e.g., omega-3 fatty acid types, sources, doses, and intervention/exposure length), and comparator(s);
cointerventions (e.g., omega-6 fatty acid use);
withdrawals and dropouts, including reasons;
clinical outcomes;
fatty acid content of biomarkers; and,
adverse events (e.g., side effects).
Question-specific summary tables embedded in the text describe each study addressing a given question in abbreviated fashion, highlighting some key characteristics, including sample size (as measure of the “weight” of the evidence and possible precision of the results), dose and type of omega-3 fatty acids, and comparators' (i.e., comparison groups') specifications. This affords a comparison of all studies addressing a given question. A study can appear in more than one summary table since it can address more than one research question. Also question-specific is each summary matrix, situating each study in terms of its study quality and its applicability.
Study quality refers to the internal validity, or methodological soundness, of a study. A systematic review can be faced with great variability in the quality of its included studies. Our approach is not to use a minimal level of quality as an inclusion criterion since this precludes assessing the possible impact of study quality on study results.
A study with low quality can make it difficult to clearly and meaningfully interpret its results, that is, to unequivocally attribute a significant observed benefit exclusively to an intervention/exposure (as opposed to other factors). Since definitions, or standards, of study quality can depend on the type of research design, different constructs were selected to evaluate, from study reports, the quality of RCTs and studies employing other types of research design. After a calibration exercise involving two studies with an RCT design, two assessors independently evaluated study quality. Disagreements were resolved via forced consensus. In the case of designs other than RCTs, a single quality assessor performed the evaluations. Time did not permit their dual assessment.
Four fundamental quality constructs from two instruments were used to rate the internal validity of RCTs. These tools were chosen collectively by the three EPCs involved in the 2-year task order because they have been validated. The Jadad items158 assess the reporting of randomization, double blinding, and, withdrawals and dropouts (Appendix C *). Total scores range from 0 to 5, with a score less than 3 indicating low quality. The reporting of the concealment of a trial's allocation to treatment159 yields three grades (A = adequate; B = unclear; C = inadequate) (Appendix C).
The assessment of the quality of studies using designs other than RCTs is complicated by the dearth of validated instruments and the variety of such designs (e.g., non-randomized controlled trials; uncontrolled studies). Nevertheless, a recent systematic review by Deeks et al. identified a number of “best tools” for use with these designs.160 Among them was a published instrument developed by Downs and Black161 and an unpublished albeit validated instrument derived by experts in Newcastle and Ottawa (NOS).162 The former validated both design-specific and design-neutral items.
Where case-control studies were included in the review, the validated NOS was employed. Items applicable to cross-sectional designs were taken from the Downs and Black instrument; or, if the required constructs were not operationalized in this instrument, they were developed as modifications of existing NOS items (e.g., single prospective cohort studies).(Appendix C).
It should be noted that the items defining the case-control assessment tool from the NOS were used as a whole, although specific guidelines as to which total score indicates either low or sound quality are unavailable. Likewise, no guidelines exist to mark low or sound study quality based on any subset of Downs and Black's 27-item instrument. As already asserted, an Jadad total quality score of less than 3 indicates low quality. To permit the entry of these quality data into a summary matrix, cutpoints for each type of design were set somewhat arbitrarily to establish three levels of internal validity (see Summary Matrix).
It was decided by our review team that, given the limitations of space, especially in print-based study reports, and the amount of detail that would likely be required to provide all of the details we needed to fully establish that only appropriate methods had been used to extract, prepare, store and analyze lipid content, it was reasonable to appraise these methods by focusing instead on identifying extant descriptions of inappropriate methods. On occasion, the inappropriateness of methods had to be determined by reference to standard protocols.
Pilot-tested exclusively for their ease of use within the data abstraction form were questions designed to informally assess the successful control of study confounding from variables identified by content experts as potential threats to the internal validity of studies pertinent to the review. In their view, these variables required experimental or statistical control to permit an uncomplicated interpretation of study results (Appendix C *). The two major categories of threat in controlled designs came from having study groups vary in terms of key prestudy or baseline characteristics (e.g., background diet), or from having certain on-study changes (e.g., unexpected illness) unrelated to the exposure or intervention, occur unequally across study groups to produce confounding. Even RCTs are not immune to being influenced by these threats to internal validity.
For example, if in a placebo-controlled RCT test of the supplemental treatment efficacy of omega-3 fatty acids, only certain treatment group members' background diets changed appreciably from what was observed at baseline (e.g., decreased fish intake and thus an increased omega-6/omega-3 ratio in the background diet), at which point the two study groups' baseline diets had been deemed comparable, then this on-study inequality could influence study outcomes. Because of this change in background diet, one study group might all of a sudden be receiving a different ratio of omega-6/omega-3 fatty acid intake than what had been set in the study protocol. This would amount to a change in the planned, on-study between-group difference in omega-6/omega-3 fatty acid intake; and, it is this intake ratio which could have the greatest influence on clinical outcomes. In general, contraventions of planned on-study between-group equivalences (e.g., caloric/energy intake; background diet; current smoker status; alcohol consumption) or of planned, on-study between-group differences (e.g., amount of omega-3 fatty acid intake) related to events other than the intervention/exposure (e.g., stressors, which can alter participants' patterns of eating, smoking, and alcohol consumption), that is, in variables with the potential to affect child and maternal health outcomes (and biomarker levels), could either “mask” or incorrectly “reveal” clinical benefits of the intervention depending on the groups in which these unexpected changes occurred. Then, unless statistical adjustments are made, such a scenario will complicate the meaningful interpretation of outcomes.
These informal assessment items were modified to assess single group studies since on-study changes involving the same key variables can also complicate the interpretation of their study results. However, no quality scores were derived from the data abstractors' responses to these questions pertaining to controlled or uncontrolled studies.
As specified in the scope of work for this series of evidence reports on the health benefits of omega-3 fatty acids, the primary focus is on the US population. Given the geographical location of the UO-EPC, however, the definition of study applicability was expanded slightly to include Canada as part of a larger North American context. This study's reference point became the “typical” North American.
Also known as external validity, or generalizability, the construct of applicability refers to the degree to which a given study's sample population is sufficiently representative of the population to which one wishes to generalize its results. In the present review, two schemes operationally defined applicability (Appendix C *). One assessed studies involving at least one otherwise “healthy” maternal population, with the other evaluating studies involving at least one otherwise “healthy” maternal population with a known elevated risk for a particular pregnancy and/or infant outcome.
With regards to the highest level of applicability (Level I) in the first scheme, the broadest definition of the population of interest is the otherwise “healthy” North American (or similar individual), drawn from a somewhat broad socio-demographic spectrum (i.e., age, race), and who eats a diet “typical” of a broad spectrum North American population (e.g., with an estimated omega-6/omega-3 intake ratio of at least 15: see below for references). For Level I applicability in the second scheme, the broadest definition of the population of interest is the otherwise “healthy” North American (or similar individual), at known risk for a particular pregnancy and/or infant outcome perhaps because of a similar past occurrence, representing a somewhat broad socio-demographic spectrum (i.e., age, race), and eating a diet “typical” of a broad spectrum North American population (e.g., with an estimated omega-6/omega-3 intake ratio of at least 15). Together, these level I definitions represent the respective reference points, with applicability decreasing as the definition of the sample study population narrows in terms of the factors represented in the two schemes.
Operationalized ideally in this review as the omega-6/omega-3 fatty acid ratio, background diet may be an important factor in assessing both types of study population (i.e., no known risk versus known risk). Given the competitive relationship between omega-3 and omega-6 fatty acids, both for enzymes to yield key metabolites with specific effects in the human biosystem (see Chapter 1) and for positions in cell membranes from which to have these and other possible influences (e.g., clinical prevention), the absolute and relative intake of omega-3 and omega-6 fatty acids from all sources, and not just from the identified exposure, likely need to be taken into account when deciding whether populations assessed in different studies are comparable. The likelihood of biological and/or clinical effects in studies may turn out to vary depending on these absolute or relative intake values. A high background dietary omega-6/omega-3 fatty acid intake ratio—potentially reflected in a corresponding differential in these contents in cell membranes—may make it harder for omega-3 fatty acid supplementation to make a clinically meaningful difference,163 although already having considerable omega-3 fatty acid content in the background diet and in cell membranes because of a low omega-6/omega-3 fatty acid intake ratio may make it difficult for typically small amounts of omega-3 fatty acid supplementation to make a clinically meaningful difference (see Discussion).
Irrespective of which of these hypotheses may be eventually confirmed elsewhere, the fact that national, and sometimes regional, populations can vary in terms of their diet's omega-6/omega-3 fatty acid intake ratio strongly suggests that this potential confounding influence on study outcomes needs to be represented in the applicability schemes whereby the North American value is the reference point. The typical North American diet contains an omega-6/omega-3 fatty acid intake ratio of at least 15, whereas urban India and Japan's corresponding values are 38–50 and 4, respectively.152, 164–175
UK populations represent somewhat of a special case in that, while they can exhibit socio-demographic pictures similarly broad to the ones seen in North American study populations, their somewhat different lifestyle and background diet recommended an applicability value of “II.” However, if participants were drawn from a narrower UK population, then a “III” was assigned. One assessor evaluated study applicability.
For a given research question, and where possible (e.g., more than one study addressing the question), a summary matrix situates the pertinent studies in terms of their respective study quality (internal validity) and applicability (external validity) values. The Jadad total quality score defined RCTs' internal validity in summary matrices. A three-level format was derived from the range of possible RCT quality scores (A = Jadad total score of 4 or 5; B = Jadad total score of 3; C = Jadad total score of 0, 1 or 2). Given that allocation concealment scores have in the past tended to vary less widely than Jadad total scores, allocation concealment values were entered as superscripts in the summary matrices.163 A similar approach was taken for the studies employing other research designs. The following cutpoints were established, albeit without benefit of a validational exercise:
case-control study (NOS): A = 9–12; B = 5–8; C = 1–4;
(multiple-group) cross-sectional study: A = 8–11; B = 5–7; C = 1–4; and,
single prospective cohort study (Modified NOS): A = 8–10; B = 4–7; C = 1–3.
The three-level applicability format was established by the 3 EPCs involved in the 2-year project for practical reasons, to permit the incorporation of quality scores within a summary matrix. Studies assigned an “X” (i.e., insufficient information to establish applicability) were excluded from summary matrices.
An overarching qualitative synthesis describes the progress of each citation, then report, through the stages of the systematic review. It also highlights certain report and study design characteristics of included studies (e.g., distributions of research design by research question). Then, for each question, a separate qualitative synthesis is derived for included evidence, organized by broad categories of research design (i.e., RCTs vs observational studies). A brief study-by-study overview typically introduces the synthesis, followed by a narrative summary of the key defining features of relevant studies (e.g., inclusion/exclusion criteria), including their populations (e.g., diagnosis-related), intervention/exposures (e.g., types of omega-3 fatty acid), cointerventions (e.g., psychotropic medication), outcomes, study quality, applicability, and results. Whether or not data can be organized according to these subheadings depends on the number of studies addressing a given question and the amount or variety of detail available in the study reports. For example, having identified too few studies per research question that exhibit significant effects for a given clinical outcome can preclude determining the impact of covariables with the potential to modify or confound study results (e.g., type or dose of omega-3 fatty acids).
Juxtaposing, in turn, all pertinent studies' parameters for a given research question has two key consequences. It allows us to identify the “gaps” in knowledge deemed crucial by content experts to understanding the clinical phenomenon (e.g., efficacy of omega-3 fatty acids). That is, data regarding possible confounders may be lacking, making it difficult to interpret study results with unfettered confidence. These gaps point to those variables requiring measurement and experimental or statistical control in future research. Second, it affords an understanding of the definition and extent of the included studies' clinical homogeneity (i.e., population, intervention, cointervention, outcome), which can then inform decisions regarding the appropriateness of meta-analysis. Where strong clinical heterogeneity is observed, it may be important to forego meta-analysis because the “population” to which any point estimate, and its measure of precision, might be extrapolated may not exist per se; it, too, is synthetic (e.g., the “average” preterm infant). Subject to scrutiny in the evaluation of cross-study clinical homogeneity is the ability of each study to control for confounding influences and yield results that can be interpreted without serious question marks. The existence of statistical heterogeneity also plays a role in the decision to do without a quantitative synthesis. Whether or not meta-analysis is considered appropriate, an attempt is made to make sense of the possible influence of covariates and confounders within the context of the qualitative synthesis.
Where eligibility criteria permit, evidence from research designs with a lesser inherent potential to control for biasing influences are used to see whether, collectively, they confirm the picture of efficacy, or association, derived from designs with a greater inherent potential to achieve this goal (e.g., RCTs: see Eligibility Criteria). For the purposes of interpreting results, greater emphasis is placed on the latter, with “greater emphasis” meaning that we assign greater interpretative, not numerical or statistical, weight to these intrinsically stronger designs. Factors other than study design also taken into account in interpreting results include study quality, the number of studies, and whether studies were sufficiently powered.
Meta-analysis was conducted providing there was a clearly defined population to which to generalize the synthetic result (and its precision). Given its greater potential to control for possible confounding factors, only RCT evidence regarding the question of efficacy/effectiveness was considered for inclusion in meta-analysis. Details concerning certain study design requirements for entry into meta-analysis are presented in the Eligibility Criteria section (see above), and are not repeated here. All things being equal, it was also assumed that priority in meta-analysis should be given to clinical outcomes evaluated using validated measures pertinent to the present day practice of medicine (e.g., respective Bayley's scales for neurological and cognitive development).
The inclusion criteria to conduct meta-analysis were:
at least two RCTs;
same population characteristics (mean age, health status, gender);
same co-interventions;
same intervention based on the type of omega-3 FA supplemented (DHA+AA vs. DHA vs. DHA+EPA, etc.) regardless of the daily dose in the child population;
same comparator based on source of placebo (e.g., olive oil, unsupplemented formula);
outcomes relevant to respond the key-questions: percentage (n) of premature deliveries, incidence of GHT, pre-eclampsia or eclampsia, incidence of IUGR or SGA infants, weight, length and head circumference of infants (means), neurological and cognitive development measured by validated scales (e.g., Bayley's Develomental Scale score), and visual acuity or visual function of infants measured by appropriate tests (Teller's Card test, etc.).
Insufficient numbers of study with comparable populations, interventions, intervention-comparator contrasts or outcomes precluded the conduct of a) many planned meta-analyses; b) planned subgroup analyses involving virtually all of the predefined covariables with the presumed potential to influence pertinent clinical-developmental outcomes (e.g., source, type or dose of omega-3 fatty acids); and c) planned sensitivity analyses investigating the possible impact of study quality and publication bias on clinical-developmental outcomes.
Decisions regarding statistical models and related issues such as statistical heterogeneity are provided where results of meta-analysis are reported.
Regardless of its source, the progress of each bibliographic record through the stages of the systematic review is illustrated in the modified QUOROM flow chart (Appendix D *). Ideally, a record included an abstract and key words, in addition to a citation. When a citation was discovered, for example, through a manual search of a reference list, its complete bibliographic record was sought (e.g., PubMed®) and then entered into the first level of relevance screening.
Of the 2,049 records entered into the initial screening for relevance, 1,579 were excluded. Reflecting the specific eligibility criteria, the reasons for exclusion were: a. did not involve human participants (n=301); b. did not involve omega-3 FAs as an exposure/intervention (n=827); c. the purpose of the exposure/intervention was not for the assessment of child or maternal health outcomes (n=253); and, d. not a primary study (e.g., a review; n=198). All of the remaining 470 reports were then retrieved and subjected to a more detailed relevance assessment. The second relevance screening then excluded 279 reports for the following reasons: a. did not involve human participants (n=15); b. did not involve omega-3 FAs as an exposure/intervention (n=101); c. the purpose of the exposure/intervention did not concern maternal or childhood health outcomes (n=69); and, d. not a primary study (e.g., a review; n=76). There were an additional number of reports not retrieved at this level (n=18). The third relevance screening took into the account the level of evidence appropriate to answer each question. A list of excluded due to level of evidence (i.e., observational studies) studies for each topic is included in the Appendix F. Of the 191 reports that made it to this level of screening, 74 were excluded. Hence, in total, 117 reports, describing 89 unique studies, were deemed relevant for the systematic review, with 20 studies each described by more than one report and three reports describing more than one unique study.
The 20 unique studies reported by more than one report were: Agostoni et al.176 (Agostoni et al.177, 178), Al et al. 1995179(Al et al.180), Auestad et al.,104 (Scott et al.104, Auestad et al.181), Birch et al.182 (Birch et al.,183 Hoffman et al.184), Carlson et al.185 (Werkman et al.,186 Carlson et al.187–190), Carlson et al.191 (Carlson et al.192), Clandinin et al.193 (secondary reports194, 195), de Groot et al.,196 (de Groot et al.197), Faldella et al.198 (Faldella et al.199), Helland et al.,141(Helland et al.200), Innis et al.201 (Diersen-Schade et al.202), Jensen et al.203 (Voigt et al.204), Makrides et al.205 (secondary report206), O'Connor et al.207 (secondary report208), Olsen et al.209 (Olsen et al.,210 Salvig et al.211), Uauy et al.212 (Uauy et al.,213 Hoffman et al.,214, 215 Birch et al.,216 Uauy et al.,217), Vanderhoof et al.218 (Vanderhoof et al.219, 220), Vilbergsson et al.221 (secondary report222), Willatts et al.223 (secondary report224), Woltil et al.225 (secondary report226).
Auestad et al.227 that included two uniques studies as well as Birch et al.228 Olsen et al. reported 6 unique trials.31
Of the 117 relevant reports describing 89 unique studies, there were 63 randomized controlled trials (RCTs) and 26 observational studies across all the key questions. As an overview, the number of included studies investigating each question are described below, distinguishing the reports by population type (maternal, preterm or term infants), by intake of omega-3 FA supplements, or by research design. Since a given study may address more than one question, some studies may be described for more than one question.
Only one study required translation from German to English.229
Fifteen uniques studies investigated the influence of omega-3 FAs during pregnancy on the duration of gestation.141, 196, 209, 230, 231, 231–235 All reports were RCTs since we had decided to exclude other research designs if enough well-conducted RCTs were identified. Eight RCTs evaluated the question regarding the influence of maternal intake of omega-3 FA during pregnancy on the incidence of gestational hypertension (GHT), pre-eclampsia or eclampsia,209, 230, 234, 236–238 whereas, 14 RCTs assessed the outcome of incidence of infants small for gestational age (SGA).141, 196, 209, 230–236, 238
Regarding the question of the association between the duration of gestation in women with or without a history of a previous preterm birth with the omega-3 or omega-6/omega-3 FA content of maternal biomarkers during pregnancy, four studies were identified—one RCT,234 one case-control study,239 one single prospective cohort study,240 and one cross-sectional study.241 Five observational studies addressed the question of the association between maternal biomarkers and the incidence of GHT, pre-eclampsia or eclampsia—one was a prospective cohort study179 and four were of cross-sectional design.229, 242–244 Whereas, one RCT,196 two case-control studies,245, 246 one single prospective cohort study240 and two cross-sectional studies241, 247 were identified that addressed the possible association between the incidence of SGA infants and the omega-3 or omega-6/omega-3 FA content of maternal biomarkers during pregnancy.
No studies were identified across all the child outcomes (i.e., growth patterns, neurocognitive development and visual function) regarding the influence of the intake of omega-3 FA from sources other than human milk, or infant formula.
Only one RCT was identified to answer the question of maternal intake of omega-3 FA during pregnancy and its influence of the growth pattern in term and preterm infants.141 One RCT,248 one prospective cohort study,249 and one cross-sectional study addressed the question of the influence of omega-3 FA content of human milk, with or without known maternal intake, on growth patterns in term infants. No studies were identified that addressed this question in the preterm population. Twenty RCTs investigated the influence of omega-3 FA content in formula, with or without human milk intake, on the growth patterns in preterm infants,185, 193, 198, 201, 207, 212, 218, 225, 250–259 whereas, 18 RCTs were conducted in term infants.104, 182, 203, 205, 223, 227, 260–270
No studies were identified regarding the association between the omega-3 or omega-6/omega-3 FA content of maternal or fetal biomarkers during pregnancy and the growth patterns of term or preterm infants. However, a total of 12 studies addressed the question of child biomarkers, of which five RCTs included a preterm population of infants,185, 191, 201, 207, 212 and five RCTs143, 203, 205, 262, 263 and one prospective single cohort study271 included a term population of infants; the Woltil et al. study, which was deliberately described only in the preterm section of this question, selected a group of very low birth weight (VLBW) preterm and term infants.225
Only one RCT was identified to answer the question of maternal intake of omega-3 FA during pregnancy and its influence on the neurological development in term and preterm infants.141 One RCT138 and one prospective cohort study evaluated the influence of omega-3 FA content of human milk, with or without known maternal intake, on the neurological development in term infants. No studies were identified in the preterm population for this particular question. Six RCTs investigated the influence of omega-3 FA content in formula, with or without human milk intake, on the neurological development outcomes in preterm infants,193, 207, 254, 270, 272, 273 whereas, eight RCTs were conducted in term infants.104, 176, 182, 203, 205, 227, 227, 265
One cross-sectional study conducted in the United States assessed the association between maternal omega-3 FA content during pregnancy and the neurological development of the infants.274 No studies were identified to assess the association between the neurological develoment in term or preterm infants and the omega-3 or omega-6/omega-3 FA content of fetal biomarkers during pregnancy. However, four RCTs176, 182, 203, 205 and one prospective cohort study271 investigated this association, but in child biomarkers.
One RCT235 and one cross-sectional study275 evaluated the question of maternal intake of omega-3 FA during pregnancy and its influence on the visual function in term and preterm infants. Two RCTs,138, 248 one prospective cohort276 and one cross-sectional study140 evaluated the influence of omega-3 FA content of human milk, with or without known maternal intake, on the visual function in term infants. No studies were identified in the preterm population for this particular question. Nine unique RCTs investigated the influence of omega-3 FA content in formula, with or without human milk intake, on visual function outcomes in preterm infants,185, 191, 198, 201, 207, 212, 251, 254, 272 whereas, 13 RCTs were conducted in term infants.104, 182, 203, 205, 227, 262–264, 266, 269, 270, 277
One cross-sectional study assessed the association between maternal omega-3 FA content during pregnancy and the visual function of the infants.275 No studies were identified to assess the association between visual function in term or preterm infants and the omega-3 or omega-6/omega-3 FA content of fetal biomarkers during pregnancy. However, 21 studies investigated this association in child biomarkers. Five studies included a preterm population,185, 198, 212, 278, 279 whereas, 16 studies included term infants. Of five studies in the preterm group, three were RCTs185, 198, 212 and two were cross-sectional studies.278, 279 Of the 16 term infant studies, nine were RCTs138, 182, 203, 248, 262–264, 269, 270 and seven were observational studies.140, 271, 275, 278, 280–282
One RCT283 evaluated the question of maternal intake of omega-3 FA during pregnancy and its influence on the cognitive development outcomes in term and preterm infants. One RCT138 and one single prospective cohort study284 evaluated the influence of omega-3 FA content of human milk, with or without known maternal intake, on the cognitive development of term infants. No studies evaluated this outcome in preterm infants.
Six RCTs investigated the influence of omega-3 FA content in formula, with or without human milk intake, on the cognitive develoment in preterm infants,185, 193, 207, 258, 272, 273 while eight RCTs were conducted in term infants.104, 182, 203, 205, 223, 227, 265 No studies were identified that evaluated the association between the omega-3 FA content of maternal or fetal biomarkers during pregnancy and the cognitive development outcomes. However, six studies addressed the question of child biomarkers. Four studies were RCTs138, 182, 203, 205 and two were single prospective cohort studies.271, 285
All of the RCT's were evaluated for safety data. In addition, two other RCTs, although not providing efficacy data, did provide safety data and hence were also evaluated.286, 287
The remainder of this chapter is organized by group of outcomes (pregnancy, growth, neurological, visual and cognitive), with the evidence addressing each of the key questions related to the type of intake, where at least one study was identified. Safety data is presented last. A table describing the composition of the interventional infant formulas used across the trials was added to Appendix G *. We begin with pregnancy outcomes.
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Olsen, 1992, Denmark: NR parallel RCT209 | 2.7g n-3 FAs fish oil (n=266) | Olive oil (n=136)/ pb (n=131) | S↑ GA in fish oil grp++ | Jadad total: 2 [Grade: C]; Schulz: Inadequate | III |
| Bulstra-Ramakers, 1994, Netherlands: 27 wks parallel RCT238 | n-3 FA-enriched capsules: EPA 3 g/d DHA NR (n=32) | Control capsules: coconut oil (n=31) | NS in % premature deliveries | Jadad total: 5 [Grade: A]; Schulz: Adequate | III |
| Onwude, 1995, UK: NR parallel RCT233 | DHA+EPA (1620mg EPA+1080mg DHA) (n=113) | pb (n=119) | NS in GA NS in % premature deliveries | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significantly different;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
GA = gestational age;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001; PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Olsen, 2000d, multicenter: 20 wks parallel RCT230 | Twins trial: Pikasol (fish oil) 0.9g DHA, 1.3g EPA capsules (n=289) | Olive oil capsules (n=290) | (ITT) NS in GA | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
| Olsen, 2000e, multicenter: 33 wks parallel RCT230 | Threat-PE: Pikasol (fish oil) 2.1g DHA, 2.9g EPA capsules (n=44) | Olive oil capsules (n=35) | (ITT) NS in GA | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
| Olsen, 2000f, multicenter: 33 wks parallel RCT230 | Susp-IUGR: Pikasol (fish oil) 2.1g DHA, 2.9g EPA capsules (n=36) | Olive oil capsules (n=27) | (ITT) S↑ GA in fish oil gp+ | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significantly different;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
GA = gestational age;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001; PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower;
Threat-PE = pregnant women with threatening preeclampsia;
Susp-IUGR = pregnant women with suspected IUGR
Olsen et al.,230 in six multicenter RCTs including 19 hospitals, examined the preventative (prophylactic) and therapeutic effects of dietary n-3 FAs on pre-term delivery, IUGR and GHT in women with an increased risk for these clinical outcomes. Four prophylactic trials enrolled women after 16 weeks of GA with an uncomplicated pregnancy who had experienced previous pre-term delivery (n=232), IUGR (n=280), or GHT (n=386) and women who were currently pregnant with twins (n=579).
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Olsen, 2000a, multicenter: 20 wks parallel RCT230 | Earl-PD: Pikasol (fish oil) 0.9g DHA, 1.3g EPA capsules (n=110) | Olive oil capsules (n=122) | (ITT) S↑ GA in fish oil gp+ S↓ % Premature delivery in fish oil gp+ | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
| Olsen, 2000b, multicenter: 20 wks parallel RCT230 | Earl-IUGR: Pikasol (fish oil) 0.9g DHA, 1.3g EPA capsules (n=141) | Olive oil capsules (n=139) | (ITT) S↑ GA in fish oil gp+ | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
| Olsen, 2000c, multicenter: 20 wks parallel RCT230 | Earl-PIH: Pikasol (fish oil) 0.9g DHA, 1.3g EPA capsules (n=184) | Olive oil capsules (n=202) | (ITT) NS in GA | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significantly different;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
GA = gestational age;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001; PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower;
Earl-PD = pregnant women with antecedent of premature delivery;
Earl-IUGR = pregnant women with antecedent of IUGR;
Earl-PIH = pregnant women with antecedent of gestational hypertention in past pregnancies
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Helland, 2001, Norway: 8 mo parallel RCT141 | CGA 1183 mg/d DHA + 803 mg/d EPA + 27.5 mg/d AA (n=301) | COG pb 8.3mg/d DHA (n=289) | NS in GA | n/a | Jadad total: 4 [Grade: A]; Schulz: Unclear | III |
| Smuts, 2003, US: 13 wk parallel RCT232 | High-DHA eggs (183.9 mg/d DHA) (n=18) | Regular-DHA eggs (35.1 mg/d DHA) (n=19) | NS in GA High-DHA eggs ↓ PTDR than control (no p-value) | n/a | Jadad total: 2 [Grade: C]; Schulz: Unclear | II |
| Smuts, 2003, US: 13 wk parallel RCT234 | High-DHA eggs (133 mg/d DHA) (n=176) | Regular-DHA eggs (33 11mg/d DHA) (n=174) | S↑ in GA in High-DHA vs Regular-DHA+ NS in PTDR | S (+) correlation between infant RBC DHA & GA+ NS correlation between maternal RBC DHA & GA | Jadad total: 3 [Grade: B]; Schulz: Inadequate | II |
Proceeding from highest omega-3, or lowest omega-6/omega-3 fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significantly different;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
CGA = cod liver oil group;
COG = corn oil group;
GA = gestational age;
PTDR = preterm delivery rate;
RBC = red blood cells;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001; PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Malcolm, 2003, Denmark: 15 wks parallel RCT235 | Fish oil (DHA 100 mg) capsules (n=50) | pb (n=50) | NS in GA | NS correlation umbilical cord DHA & GA | Jadad total: 3 [Grade: B]; Schulz: Unclear | II |
| Dunstan, 2004, Australia: 19 wk parallel RCT231 | LCPUFA (2.2 g/d DHA + 1.1 g/d EPA) (n=40) | pb (n=43) | NS in GA | NS correlation between infant RBC DHA, EPA, AA & GA | Jadad total: 3 [Grade: B]; Schulz: Unclear | III |
| de Groot, 2004, Netherlands: 24 wk parallel RCT196 | LCPUFA (9.02 g/d LA+2.82 g/d ALA) (n=40) | pb (10.94 g/d LA+0.03 g/d ALA) (n=39) | NS in GA | n/a | Jadad total: 3 [Grade: B]; Schulz: Unclear | III |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significantly different;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
GA = gestational age;
RBC = red blood cells;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower;
LA = linoleic acid;
ALA = alpha-linolenic acid;
Study characteristics. Only the study of Olsen et al. had more than two study groups.209 Countries where the studies were conducted included the United States,232, 234 the United Kingdom,233, 235 The Netherlands,196, 238 Australia,231 Denmark209 and Norway.141 One multicenter study involved six trials conducted in 19 centers in Denmark, Scotland, Sweden, England, The Netherlands, Norway, Belgium and Russia.230
Both of the studies by Smuts et al.232, 234 were financially supported by Market Biosciences Boulder Corporation (former Omega Teach Inc.), Boulder, Colorado. The study by Onwude et al.233 was sponsored by Yorkshire Region Locally Organized Research, Glaxo (Leeds) and Seven Seas (Hull). Olsen et al.'s studies230 were funded by Conserted Action and PECO programmes of European Comission and the Danish National Research Foundation. The study of de Groot et al.196 was supported by Unilever Research and Development (Vlaardingen, Netherlands). Dunstan et al.'s231 was funded by the NH and MRC and Raine Medical Research Foundation, Australia. The other study by Olsen et al.209 was supported by the Danish Medical Research Council, Sygekassernes Helsefond, Weman's Legat and Michaelsen Fonden. The study by Helland et al.141 was financed by Peter Moller, Avd. Orkla ASA and “Aktieselskabet Freia Chocoladefabriks Medicinske Fond.” Malcolm et al. was supported by the Chief Scientist's Office, Scottish Office Health Department.235 Finally, Bulstra-Ramakers et al. failed to provide this information.238
Population characteristics. There was a total number of 3,686 pregnant women enrolled across the fifteen trials. The sample size varied from as low as 37232 to 590141 women. However, Helland et al. analysed only the patients who completed the study (n=341 of 590, 57%).288 The mean age-range of study participants across the eight studies was 19.9 (SD=4.1) years to 32.9 (SD=14.6) years. Participants in both of the Smuts et al. trials232, 234 tended to be younger (mean age range for high-DHA egg group=19.9 [SD=4.1] to 21.7 years; mean age range for placebo group=21.6 [SD=4.2] years to 24.8 [SD=7.8] years) than the participants in the rest of the studies (mean age range for treatment groups=27.6 [SD=3.2] years, and 32.9 [SD=14.6] years for the placebo groups).141, 196, 209, 230, 231, 233 Two trials did not provide this information.235, 238
A thorough description of both inclusion and exclusion criteria were given in all trials. Information about racial/ethnic backgrounds were given in three of the 15 studies.196, 232, 234 Study participants in two trials were predominantly of African-American descent, comprising 79% and 73% of participants in the ordinary egg groups, and 83% and 73% of participants in the high-DHA egg groups, respectively.232, 234 Only White participants were recruited in the Groot et al. study.196
The exact duration of maternal dietary intervention during pregnancy and/or breastfeeding was reported in all but two studies,209, 233 and ranged from 5 weeks230 to 8 months.141 In most of the studies, LCPUFA supplementation was prescribed in the second trimester of pregnancy.141, 196, 231, 233, 235, 238 In three studies, PUFA supplementation was administered from the third trimester until delivery.209, 232, 234 There was no study where participants were randomized from the first trimester. In one of the studies of Olsen et al., four prophylactic groups of pregnant women were randomized from gestational week 20, whereas, in the therapeutic trials women were randomized around gestational week 33.230 Detailed information about the duration of the LCPUFA supplementation is provided in the Evidence Tables (Appendix E *). Maternal social status, defined as years of education, was determined in two studies.141, 196
Information regarding maternal smoking history and/or smoking during pregnancy was provided in eleven studies.141, 196, 209, 230, 233, 234 Alcohol consumption at 14 weeks of pregnancy was reported in one study.196
In the majority of RCTs, there was no evidence that randomization failed to produce comparable groups in terms of previous obstetric history, socioeconomic status, dietary intake of fish, smoking habits, alcohol intake, body mass index and GA.141, 209, 231, 234, 235, 289 Onwude et al. showed that significantly more women were current smokers at enrollment in the treatment group than in the placebo group.233 Smuts et al. reported that women assigned to consume ordinary eggs were significantly older than those in the high-DHA egg group.232 Olsen et al. reported that in women with suspected IUGR, those in the placebo group had significantly higher GA after randomization.230
Intervention/exposure characteristics. Across the 15 studies, the sources of omega-3 LCPUFA were identified as being either from natural feeding sources, such as eggs, fish and margarines, or from manufactured medical supplementations, such as capsules containing fish oil. Eggs as a source of omega-3 FA were used in two studies232, 234 and margarine, containing different amounts of LA and ALA, was used in one study.196
Gelatin capsules containing a fish oil were utilized in 11 studies. In most of the studies, LCPUFA supplementation was prescribed in the second trimester of pregnancy.141, 196, 231, 233, 235, 238 In three studies, PUFA supplementation was administered from the third trimester until delivery.209, 232, 234 There were no studies where participants were randomized from the first trimester. In one of the studies of Olsen et al., four prophylactic groups of pregnant women were randomized from gestational week 20, whereas, in the therapeutic trials women were randomized around gestational week 33.230
Detailed information about the duration of the LCPUFA supplementation209, 230, 231, 233, 235, 238 is provided in the Evidence Tables (Appendix E). Helland et al. failed to report the manner in which study participants received their oil supplementation;141 however, the investigators were the only ones to identify the exact sources of dietary FAs (i.e., cod liver oil and corn oil as the placebo). The daily amount of omega-3 LCPUFA intake, as well as the start and duration of intake, varied across the studies.
Pregnant women in the Bulstra-Ramakers et al. study received four capsules containing 0.25 mg EPA or placebo (coconut oil) three times daily. The EPA capsules contained a mixture of 3 g EPA and DHA. Both capsules were similar in appearance, smell and taste.238
The two Smuts et al. studies232, 234 used similar regimens of FA supplementation for the high-DHA eggs and the ordinary egg groups. Daily DHA intake was reported to be 183.9 (SD=71.4) mg in the high-DHA diet and 35.1 (SD=13.2) mg for placebo in the one study232 and 133 (SD=15) mg and 33 (SD=11) mg, respectively, in the other Smut et al. study.234 Women in both studies were randomized to the different dietary groups in their third trimester of pregnancy (24 to 28 weeks), for a mean duration of supplementation of approximately 13 weeks.232, 234
de Groot et al. randomized a sample of women to receive margarine containing different amounts of LA and ALA from week 14 of GA until delivery.196 The experimental group received 9.02 g LA and 2.82 g ALA per day, whereas, the control group received 10.94 g LA and 0.03 g ALA daily.196
Pregnant women in the Onwude et al. study were randomized to receive either fish oil or placebo.233 Women were allocated to treatment groups at a very wide range of GA, ranging from 18 to 32 weeks (mean of 24 weeks). Hence, the time of exposure to the intervention was not equal for the study participants. Women in this study were instructed to take nine capsules daily, each containing either 180 mg EPA and 120 mg DHA (treatment group), or air (placebo group); timing of the intake of the nine capsules was left to the participants.233
The patients in the Olsen et al. study received fish oil (Pikasol containing EPA [32wt%] and DHA [23wt%]) or olive oil as placebo (oleic acid [72wt%] and ALA [12wt%]), provided in 1 g identical-looking gelatine capsules, but which were not identical in taste.230 In the four prophylactic trials, four capsules of either oil were given per day, while in the two therapeutic trials, nine capsules were given per day. In the prophylactic trials women were randomized around gestational week 20, whereas, in the therapeutic trials women were randomized around gestational week 33. The same sources of intervention with the same regimen were used in the other study of Olsen et al.209
The pregnant women in the study of Malcolm et al. received two fish oil capsules, rich in DHA (Marinol D40, 100 mg DHA per capsule, R.P. Scherer Ltd, Swindon, UK) per day or identical sunflower oil placebo capsules without DHA or ALA.235 Maternal diet, including fish intake, was assessed by interview at 15 and 28 weeks of pregnancy and delivery.235
The 98 women with a history of rhinitis or asthma in the Dunstan et al. study were randomized to receive either 4 g/day of fish oil or olive oil in capsules, as a supplement to their usual diet from 20 weeks gestation until delivery, when supplementation was ceased.231 Women in the fish oil group consumed about 1.1 g EPA and 2.2 g DHA daily. All capsules contained α-tocopherol (3–4 mg/g oil) as an antioxidant.231
Helland et al. randomly assigned 590 study participants to either a treatment group (10 mL cod liver oil/day; Peter Moller, Avd Orkla, Oslo, Norway) or a placebo group (10 mL corn oil/day).141 Women in the cod liver oil group consumed 1,183 mg DHA, 803 mg EPA and 27.5 mg AA daily compared with 8.3 mg DHA in the placebo group. Randomization started at 17 to 19 weeks of gestation and supplementation continued until approximately 3 months after delivery, for a total of approximately 8 months of exposure.141
Dietary intake information was not well documented in all studies. There was no clear data to suggest that all eight studies were equally able to eliminate the possible confounding influence of having unequal amounts of calories (i.e., as energy) provided to their different study groups. Information about caloric balance of food intake among the study groups was reported in only one RCT.141 The daily energy intake (expressed as MJ/day) of participants in the Helland et al. study was similar among the two diet groups and varied from 8.2 (SD=2.0) MJ/day at week 18 of pregnancy to 8.7 (SD=2.3) MJ/day at week 35 of pregnancy.141
None of the study investigators made an effort to deodorize the LCPUFA supplementation. In the study by Smuts et al., attempts were made to maintain blinding by conducting their own sensory test with clinic nurses who were blinded to the egg source. All of the nurses felt that the omega-3-fortified eggs looked and tasted like the non-enriched eggs.232
Attempts to optimize and assess the compliance of the study participants were made in twelve trials.141, 196, 209, 230, 232, 233, 235 In all of these studies, women were asked to fill a food-frequency questionnaire indicating the exact amount of assigned dietary supplement consumed, followed by conversion of this information into dietary intake using either a computer program196 or simple percentage calculations.209, 230, 233 Smuts et al. utilized phone interviews with the women since few participants were compliant with the request to keep written records of their food intake.232
The manufacturer of the omega-3 intervention was reported in seven trials.141, 196, 209, 231, 232, 235 Purity data on the exposures used were not provided in any of the 15 studies. In five of seven studies that evaluated the FA content of biomarkers, appropriate methods to extract, prepare, store or analyze lipids were described.196, 231, 232, 234 Helland et al. gave little information about the details of blood FA composition analysis.141 None of the trials reported details as to whether, or how, the presence of methylmercury was tested or eliminated from the omega-3 FA exposure when fish oil was the source.31, 41, 290
Cointervention characteristics. Three studies reported the use and/or LCPUFA content of additional vitamin and mineral supplements taken by the pregnant participants.141, 231, 234 Smuts et al. reported that prenatal vitamin use in ordinary and high-DHA groups was 83.2% and 84.6%, respectively.234 Helland et al. reported that the amount of fat-soluble vitamins was identical between the two oil groups i.e., 117 μg/mL vitamin A; 1 μg/mL vitamin D; and, 1.4 μg/mL of dl-α-tocopherol.141 Dunstan et al. used α-tocopherol as an antioxidant to stabilize omega-3 FAs.231 No studies reported the prestudy medication use by either pregnant or breastfeeding mothers. On-study antihypertensive therapy to treat GHT was used in one of the Olsen et al. studies.230
Outcome characteristics. Fourteen studies addressed the question of whether or not omega-3 FA supplementation affects the duration of gestation (gestational age as mean±SD). Preterm delivery rate was assessed in 11 trials.41, 230, 232, 234, 291, 292 However, three more studies reported the number of premature deliveries excluded from the analysis (reported as dropouts).288, 290, 293 The use of ultrasound in the second trimester of pregnancy to determine GA was reported in four studies.209, 230, 233, 234 If the ultrasound measurement was not available, the length of gestation was estimated from the date of last normal menstrual period.209, 230 In seven studies, preterm delivery was defined as delivery at an estimated GA of less than 37 weeks.230, 234
| Study Quality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| A | B | C | ||||||||
| Applicability | I | Author | Year | n | Author | Year | n | Author | Year | n |
| II | Author | Year | n | Author | Year | n | Author | Year | n | |
| OnwudeA | 1995 | 233 | SmutsI | 2003 | 350 | SumtsU | 2003 | 73 | ||
| MalcolmU | 2003 | 100 | ||||||||
| III | Author | Year | n | Author | Year | n | Author | Year | n | |
| Bulstra-RamakersA | 1994 | 68 | DunstanU | 2004 | 98 | OlsenI | 1992 | 533 | ||
| HellandU | 2001 | 590 | De GrootU | 2004 | 79 | OlsenA | 2000 | see below* | ||
n = number of allocated/selected participants
RCT = Adequate vs UUnclear allocation concealment
= Inadequate
Olsen 2000 6 trials: a) n=232; b)=280; c)n=579; d) n=386; e) n=79; f) n=63
Randomization method was not clearly reported in four trials,290, 293–295 eight trials were not double-blinded,31, 41, 296 while double-bliniding method was not reported across five trials.288, 290, 293–295 Reasons for dropouts were not reported across eight trials.31, 41, 294
Ten studies evaluating the influence of LCPUFA supplementation on the duration of gestation, did not find any beneficial effect of omega-3 FAs over their comparators.141, 196, 230–235 Conversely, the other four studies found that dietary modifications by LCPUFA significantly prolonged the duration of gestation.209, 230 However, the population characteristics, as well as the interventions, were different across these studies. The preterm delivery trial of Olsen et al. found a significantly increased mean duration of gestation in the treatment group (fish oil) of mothers with a preterm delivery in a previous pregnancy compared with mothers in the placebo group.230 Preterm delivery rate was not affected by omega-3 FA supplementation during pregnancy and was not statistically different in randomized groups in ten trials that evaluated this outcome.31, 209, 233, 234, 238 Smuts et al. on the other hand, observed that 5.6% of women in the high-DHA group had a premature delivery compared with 25% in the control group (no statistical significance was reported).232
Dunstan et al. did not find any statistically significant relationship between GA and neonatal RBC DHA, EPA, and AA content.231 Contrary to these findings, Smuts et al.234 observed a statistically significant positive correlation between infant RBC DHA content at delivery and GA in the treatment group, whereas, maternal RBC phospholipid DHA content at the time of delivery was not significantly correlated with GA in either the treatment or placebo groups.231 Malcolm et al. measured umbilical cord plasma DHA levels in infants of supplemented mothers and observed that the duration of gestation was significantly greater in infants in the upper quartile for cord blood DHA compared with infants in the lower quartile. However, gestational length did not differ based on quartiles of umbilical cord RBC DHA.235
Meta-analysis was performed for incidence of premature deliveries, given that represents the most clinically relevant. Eleven of 15 trials reported this particular outcome. Eight of ten compared the use of DHA+EPA capsules intake with olive oil (control group).31, 41, 291 Olsen et al. 2000 reported the pooled data of six different RCTs, including pregnant women with different risk for prematurity.31 Five of eight trials provided the intervention from the second trimester (week 22) until delivery,31, 291 and three trials from week 30–33 until delivery (3rd Trimester).31, 41 Subgroup analysis (by risk of prematurity) was not possible for this outcome given the lack of individual data from Olsen et al. 2000.31
Two studies by Smuts et al. comparing the use of eggs with high DHA content (mean 133 mg DHA per egg)296 or 12 high-DHA hen eggs (135 mg DHA/egg)294 with ordinary eggs (low DHA content: 18–33 mg DHA/egg)294, 296 from the second trimester to delivery reported the incidence of premature delivery as an outcome.
Two other studies compared the use of EPA alone292 or DHA+AA (from cod oil)288 with control, yet pooling was not possible due to the difference in omega-3 FA content.
Meta-analyses for incidence of prematurity were performed by using a random effect model for odds ratio.
From eight RCTs, the incidence of premature deliveries did not differ significantly between groups, OR: 0.88 (95% CI: 0.62–1.25), p=0.47.
From two RCTs,294, 296 the incidence of premature deliveries did not differ significantly between groups, OR: 0.53 (95% CI: 0.13–2.29), p=0.40.
Olsen et al. adjusted the duration of gestation for fish consumption, as well as for compliance to the oil supplementation.209 Differences between groups in the average duration of gestation were significantly correlated with increasing fish consumption, with the mean length of gestation highest in the fish-oil group and lowest in the olive-oil group. The difference between fish oil and olive oil was nonstatistically significant between compliers and noncompliers.209
Helland et al. adjusted the duration of gestation for the concentration of DHA in umbilical plasma phospholipids and reported that neonates with high concentration of DHA in umbilical plasma phospholipids (upper quartile) had longer gestational length than neonates with low concentration.141
Onwude et al. stratified the results by use of tobacco, failing to observe a difference between groups.233
Smuts et al. adjusted the results by smoking status, maternal BMI and number of prior pregnancies.234 The duration of gestation was significantly longer in the high-DHA egg group in the nonsmoking women, and when adjusted by maternal BMI and parity.234
The power analysis was reported in nine trials,31, 288, 292, 296 while the intention-to -treat analysis approach was reported in six trials from the same author.31
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| D'Almeida, 1992, Angola: 24 wk parallel RCT236 | n-3 FA-enriched capsules: fish & primrose oil EPA 0.15 g/d DHA 0.08 g/d (n=50) | Mg2+ oxide capsules: 1 g/d (n=50)/ olive oil capsules: (n=50) | Rate of GHT ↑ in grps 1–3 vs. grp 2 (p = NR) Rate of preeclampsia/eclampsia ↑ in grp 3 vs. grps 1–2+++ | Jadad total: 2 [Grade: C]; Schulz: Inadequate | III |
| Laivuori, 1993, Finland: 8 wk parallel RCT237 | n-3 FA-enriched capsules: fish oil EPA 1.80 g/d DHA 1.20 g/d (n=5) | Primrose oil capsules: LA 3.75 g/d GLA 0.45 g/d (n=7)/ maize-olive oil capsules: 10 g/d (n=6) | NS BP, proteinuria, & rate of edema (grp 1 vs. grps 2–3) | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
| Bulstra-Ramakers, 1995, Netherlands 27 wks parallel RCT238 | n-3 FA-enriched capsules: EPA 3 g/d DHA NR (n=32) | Control capsules: coconut oil (n=31) | NS rate of GHT (grp 1 vs. grp 2) | Jadad total: 5 [Grade: A]; Schulz: Adequate | III |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
GLA = gamma-linolenic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significantly different;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
wt = weight;
RBC = red blood cells;
PL = phospholipid;
CPG = choline phosphoglycerides;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
GHT = gestational hypertension;
BP = blood pressure;
GHT = gestational hypertension
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Onwude, 1995, UK: 14 wks parallel RCT233 | n-3 FA-enriched capsules: fish oil EPA 1.62 g/d DHA 1.08 g/d (n=113) | Control capsules: air-filled (n=119) | NS rate of GHT (grp 1 vs. grp 2) | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
| Olsen, 1992, Denmark: NR parallel RCT209 | n-3 FA-enriched capsules: fish oil EPA 1.30 g/d DHA 0.90 g/d (n=266) | Control capsules: olive oil 4 g/d LA 12% (n=136)/ placebo capsules: no oil (n=131) | NS in BP or rates of GHT & preeclampsia (grp 1 vs. grps 2–3) NS in BP (grp 1 vs. grps 2–3) | Jadad total: 2 [Grade: C]; Schulz: Inadequate | III |
| Olsen, 2000, multicenter* 20 wks parallel RCT230 | Twins trial: n-3 FA-enriched capsules: fish oil EPA 1.30 g/d DHA 0.90 g/d (n=289) | Control capsules: olive oil 4 g/d LA 12% (n=290) | (ITT) NS in rates of GHT & preeclampsia (grp 1 vs. grp 2) NS BP (grp 1 vs. grp 2) | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
| Olsen, 2000, multicenter* 20 wks parallel RCT230 | Earl-PIH: n-3 FA-enriched capsules: fish oil EPA 1.30 g/d DHA 0.90 g/d (n=184) | Control capsules: olive oil 4 g/d LA 12% (n=202) | (ITT) NS in rates of GHT & preeclampsia (grp 1 vs. grp 2) NS in BP (grp 1 vs. grp 2) | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
| Smuts, 2003, US: 16 wks parallel RCT234 | n-3 FA-enriched eggs: DHA 0.23 g/d (n=142) | Control regular eggs: DHA 0.056 g/d (n=149) | NS in rates preeclampsia (grp 1 vs. grp 2) | Jadad total: 3 [Grade: B]; Schulz: Inadequate | II |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
GLA = gamma-linolenic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significantly different;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
wt = weight;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
GHT = gestational hypertension;
BP = blood pressure;
Denmark, Scotland, Sweden, UK, Italy, Netherlands, Norway, Russia, Belgium
D'Almeida et al. evaluated the effect of dietary supplementation with fish oil in preventing preeclampsia in pregnant primiparous and multiparous women with GA of less than 4 months.236
Study characteristics. Of the eight RCTs, seven were double-blinded studies209, 230, 233, 234, 236, 238 of which, one was partially double-blind.236 For one study,237 it was not clear whether the study authors used a single or double-blind design. Authors of all eight trials reported inclusion criteria. Of the eight trials, two trials failed to report their exclusion criteria.236, 237 Three trials209, 236, 237 had three arms and the remaining five trials230, 233, 234, 238 had two arms. All arms in the three-arm trials were randomized.
The studies were conducted in the following countries: the Republic of Angola,236 Finland,237 the Netherlands,230, 238 England,230, 233 Denmark,209, 230Norway,230 Russia,230 and, the U.S.234 All but two studies237, 238 reported their funding source. These included: Efamol, Ltd;236 Yorkshire Region Locally Organized Research, GLAXO (Leeds) and Seven Seas (Hull);233 Danish Medical Research, Sygekassernes Helsefond, Weiman's Legat and Michaelsen Fonden;209 Concerted Action and PECO programmes of the European Commission and the Danish National Research Foundation;230 and, Martek Biosciences Boulder Corporation (formerly OmegaTech, Inc).234
Population characteristics. The total number of enrolled pregnant women across the included studies was 2,335 and ranged from 18237 to 579230 participants.
In general, participants included in most of the trials were healthy, with uncomplicated pregnancies. Patients in the Laivuori et al. trial were diagnosed with preeclampsia (GHT and protein in urine >0.5 g/d).237 The study sample in another trial consisted of healthy women with previous history of anemia (27%), sickle-cell disease (34%), malaria (67%), or GHT (21%).236 Four trials230, 233, 236, 238 included pregnant women who had a history of GHT. In three trials,230, 233, 238 a previous episode of GHT was defined by a diastolic BP ≥90 mm Hg233, 238 or >100 mm Hg.230 The proportion of women with a previous history of GHT in the four trials ranged from 21%236 to 100%230 of participants. The between-arm proportions of women with a previous history of GHT were not similar in the study of Bulstra-Ramakers et al. (75% vs 48.4%).238 In another trial, the distribution of women with a previous history of GHT between the two randomized arms was more balanced (31.8% vs. 33.6%).233
The age of the study participants was not reported in one study.238 In the remaining studies, the age ranged from 14 236 to 40 years.233, 236, 237 The approximate mean age values across the trials209, 230, 233, 234, 237 ranged from 26.5233 to 31.0 years,237 and were similarly distributed across the treatment groups.
The women's baseline mean diastolic BP across the trials209, 230, 233, 234 ranged from 64234 to 74 mm Hg.230 In these trials, the mean values of diastolic BP were similar across the randomized arms. The baseline mean (arm-specific) systolic BP was reported only in two studies,209, 234 and ranged from 111234 to 124 mm Hg.209 In both trials, the randomized arms had similar mean values of systolic BP.
All trials reported the GA of the study participants at enrollment, randomization and start of intervention. The women's GA at enrollment and randomization across the trials, ranged from 16209, 236 to 37 weeks.237 The range of GA was reported in four trials.233, 234, 237, 238 The arm-specific mean GA (SD) was reported in five studies,230, 233, 234, 237 which was distributed evenly across the randomized arms. Three trials included only parous women (those with previous live births).230, 233, 238
The proportion of parous women across the remaining trials ranged from 48.5%230 to 67.8%209 of participants and were similar across the study arms. Five studies reported on maternal tobacco smoking.209, 230, 233, 234 The proportion of tobacco smokers ranged from 22%230to 32%209, 230, 233 of participants. In three trials,209, 230, 234 the arm-specific distributions of smokers were more or less comparable. However, in two other trials,230, 233 the proportions of smokers across the randomized arms were not as similar—in the Onwude et al. trial,233 42% of participants in the fish oil arm were smokers compared with 32% in the placebo arm; in the Olsen et al. “Earl-PIH” trial, 19.1% of participants in the fish oil arm were smokers compared with 24.2% in the placebo arm.230
The trials excluded subjects who had diabetes,230, 233, 234, 238 systemic lupus erythematosus,234, 238 chronic hypertension,233, 234 placental abruption,209, 230, 233 asthma,233 severe fetal malformation,230 drug and/or alcohol abuse,230 regular intake of fish oil,196, 209, 230, 231 allergy to fish oil,209 chronic illness (cardiovascular, cancer, renal, psychiatric, or neurological disorder) and a serious infectious disease (hepatitis).234 Regular users of prostaglandin inhibitors were also excluded.209
Intervention/exposure characteristics. In all but one study,234 the experimental intervention was dietary supplementation with omega-3 FA-enriched capsules. In the study by Smuts et al.,234 women were assigned to receive omega-3-enriched eggs. The daily number of assigned capsules across the trials varied from 4209, 230 to 12.238 Five trials209, 230, 236, 237 reported fish oil as a primary source of omega-3 FAs (i.e., ALA, LA EPA, DHA). The experimental intervention in most of the trials consisted of the combined supplementation with DHA and EPA.209, 230, 233, 236–238 The enriched eggs in the trial of Smuts et al. provided DHA only.234 In three trials,209, 230 the relative contents of DHA and EPA in each experimental capsule were 23% and 32%, respectively. In two trials,233, 237 each experimental capsule contained 120 mg and 180 mg of DHA and EPA, respectively. In two other trials,209, 230 the absolute amounts of DHA and EPA were 225 mg and 325 mg per experimental capsule, respectively. In one trial, each capsule contained 250 mg of EPA.238
The daily dose of DHA and EPA differed across the studies. The range of daily DHA intake was 0.08 g236 to 1.20 g237 and 0.15 g236 to 3.00 g238 for EPA. Three trials had a control arm with standard intervention such as magnesium oxide tablets (37 mg GLA),236 preglandin capsules (45 mg GLA)237 or olive oil209, besides the experimental and placebo arms. In seven trials, intervention in the control/placebo arms consisted of capsules with an identical appearance and taste as the experimental capsules. In these trials, placebo capsules contained olive oil,209, 230, 236, 237 maize oil,237 coconut oil,238 or no oil.233 In the trial conducted by Smuts et al., omega-3-enriched eggs contained a mean of 33 [range 22–51] mg of DHA.234
Information about patient compliance (numbers of partially- or non-compliant participants and/or reasons for non-compliance) were reported in six trials.209, 230, 233, 234, 238 The type of analysis performed (i.e., ITT) were reported in three trials.230, 233 All three studies used ITT analyses. Two trials236, 237 did not report any information on the rates and/or reasons of compliance.
The manufacturers of the omega-3 FA-enriched supplemental products in the eight studies were: Efamol Research Institute and Efamol, Ltd (England);236 Orion OY (Finland);237 Lube Ltd. (Denmark);209, 230 and, OmegaTech, Inc. (Bouldwer, CO)/Gold Circle Farms (U.S.).234 Two trials did not report the names of manufacturers who provided the omega-3 FA-enriched capsules.233, 238 The trials had varying lengths of intervention (in weeks) i.e, 24,230, 236 27,238 1 to 8,237 14 to 16233, 234 and 9.209
Cointervention characteristics. Olsen et al.'s “Earl-PIH” and “Twins” trials allowed 2 mg tocopherol/mL in the fish oil capsules only.230 Only two studies assessed the background diet of participants during the study.209, 236 Olsen et al. used a simple food-frequency questionnaire, reporting the amount of fish consumed before the trial: the low-fish intake group (at most one fish snack per month) to high fish intake (at least four fish meals per month). More than 50% of the women (n=327) were in the middle category of fish intake.209 D'Almeida et al. measured background diet with a 24-hour dietary recall questionnaire.236
Outcome characteristics. The incidence (or recurrence) rate of GHT was the primary outcome investigated in six trials.209, 230, 233, 236, 238 The definition of GHT varied slightly across the trials. Most trials defined GHT as diastolic BP above 90 mm Hg.209, 230, 233, 238 These definitions were based on the number of measurements taken and the time-interval between measurements. One trial236 defined GHT as a rise in diastolic BP of >15 mm Hg, whereas, another study238 defined it as a rise in diastolic BP of >25 mm Hg. D'Almeida et al., defined GHT as a rise in systolic BP >30 mm Hg and/or a rise in diastolic BP >15 mm Hg.236 Since one of the trials of Olsen et al.230 included only pregnant females with a previous history of GHT (BP >100 mm Hg), the outcome of interest was the recurrence (not incidence) rate of GHT (BP >90 mm Hg). Note that, in this trial, the definitions for the previous/prevalent and incident GHT, differed.
Five trials investigated the incidence of preeclampsia.209, 230, 234, 236 Of these, four trials reported the definition of incident preeclampsia.209, 230, 236 D'Almeida et al. defined preeclampsia as the simultaneous occurrence of the clinical triad: GHT, proteinuria, and edema.236 However, in the remaining three trials,209, 230 the definition was restricted to GHT accompanied only by proteinuria (proteins >0.3 g/L). Only D'Almeida et al.236 investigated the incidence of eclampsia which was defined by the simultaneous presence of GHT and two convulsive episodes.
Systolic and/or diastolic BP (measured in mm Hg), as the outcome of interest was assessed in four studies.209, 230, 237 The cumulative incidence rates of proteinuria and edema were explored in two trials.236, 237
| Study Quality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| A | B | C | ||||||||
| Applicability | I | Author | Year | n | Author | Year | n | Author | Year | n |
| II | Author | Year | n | Author | Year | n | Author | Year | n | |
| OnwudeA | 1995 | 233 | SmutsI | 2003 | 350 | |||||
| III | Author | Year | n | Author | Year | n | Author | Year | n | |
| Bulstra-RamakersA | 1994 | 68 | D'AlmeidaI | 1992 | 150 | |||||
| LaivuoriA | 1993 | 18 | ||||||||
| OlsenA | 2000 | 579* | ||||||||
| OlsenA | 2000 | 386** | ||||||||
| OlsenI | 1992 | 533 | ||||||||
n = number of allocated/selected participants
RCT = Adequate vs UUnclear allocation concealment; I Inadequate
“Earl-PIH” trial
“Twins” trial
Six trials investigating the effect of omega-3 FA-dietary supplementation on the incidence rate of GHT209, 230, 233, 237, 238 showed a nonstaistically significant difference between-groups in the incidence of GHT. In contrast, D'Almeida et al. observed that women randomized to receive the diet enriched with magnesium oxide had lower incidence rates of GHT compared with those participants in the omega-3 FA-supplemented and placebo groups (4% vs 18% and 26%, respectively; p-value NR).236
Three trials demonstrated an effect of omega-3 FA-dietary supplementation in reducing risk of preeclampsia.209, 230, 234 The mean number of women who had developed preeclampsia in all study arms was 15 (range from five to 28 women). Although the proportion of women developing preeclampsia tended to be lower in the experimental/omega-3 FA-supplemented arms,209, 230, 234 the statistical power of these trials was too low to detect these differences. Only one trial236 was able to show that women in the fish oil arm had a lower rate of preeclampsia than those in the placebo and magnesium oxide groups. In the D'Almeida et al. study, none of the women in the fish oil and magnesium oxide groups developed severe eclampsia compared with 3/50 (2.1%) patients in the placebo group.236
The findings of Laivuori et al. suggested that dietary supplementation with fish oil did not have any effects on BP, proteinuria, and edema in women with preeclampsia in 12 of 18 women enrolled.237 Findings from trials that measured BP during the follow up,209, 230 suggested that dietary supplementation with omega-3 FAs did not affect the BP of the women i.e., randomized groups had similar BP (systolic and diastolic) readings at follow up.
The cumulative incidence rates of proteinuria and edema were measured in two studies.236, 237 D'Almeida et al. found similar incidence rates of proteinuria in the randomized groups. However, women in the placebo group had a significantly higher rate of edema than those in fish oil/primrose oil and magnesium oxide groups (58% vs 26% and 24%, respectively).236 Three studies reported data on dropouts and withdrawals with different detail.233, 234, 238 The number of non-completers across the trials ranged from 1233 to 57.234
In total, seven studies were identified by our search that reported on incidence of pre-eclampsia or GHT. After examining the studies for source of oil and duration of supplementation, five studies209, 230, 233, 236, 237 were initially considered for meta-analysis.
Upon further examination, three studies209, 236, 237 were excluded. Lavuiori et al. did not report quantitative outcome data.237 D'Almeida et al. included a population with unique comorbities in a developing-world population.236 Olsen et al. was carried out in a healthy population (i.e., women not at high risk of pre-eclampsia/GHT).209 Thus, two studies230, 233 reporting on the incidence of GHT were available for meta-analysis.
Meta-analysis was performed using a random-effects model for odds ratios (n/N = number of patients with GHT/total sample in each arm).
In two studies,230, 233, the overall size of the effect was nonstatistically significant between the DHA+EPA and the control groups in the incidence of GHT (OR: 1.07, CI 95%: 0.75; 1.51).
None of the included studies reported the use of multivariable techniques such as logistic or Cox regression modeling in order to adjust for the effects of dietary supplementation on the dichotomous outcomes (GHT, preeclampsia/eclampsia). Most of the studies reported having used a Chi-square or Fisher's test. In one study,238 the randomized groups were not balanced with respect to the important prognostic/predictive factor such as a history of previous GHT (i.e., 75% vs 48.4%). The trial conducted by D'Almeida et al.236 did not report the arm-specific proportions of women with a previous history of GHT. It is not clear whether the study authors adjusted the effect of interest for any between-group differences with respect to the proportion of women with GHT.
The power calculation was reported in four trials,31, 292, 296 while the intention-to treat analysis approach was reported in two trials.31
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| D'Almeida, 1992, Angola: 24 wk parallel RCT236 | n-3 FA-enriched capsules: fish & primrose oil EPA 0.15 g/d DHA 0.08 g/d (n=50) | Mg2+ oxide capsules: 1 g/d (n=50)/ olive oil capsules: (n=50) | % <2,000 g at birth: pb 3.3% vs. n-3: 1.3% vs. Mg2+: 4.7% (no p-value) | Jadad total: 2 [Grade: C]; Schulz: Inadequate | III |
| Olsen, 1992, Denmark: NR parallel RCT209 | 2.7g n-3 FAs fish oil (n=266) | NR olive oil (n=136)/ pb (n=131) | NS birth wt | Jadad total: 2 [Grade: C]; Schulz: Inadequate | III |
| Bulstra-Ramakers, 1994, Netherlands 27 wks parallel RCT238 | n-3 FA-enriched capsules: EPA 3 g/d (n=32) | Control capsules: coconut oil (n=31) | NS in IUGR recurrence rate (grp 1 vs. grp 2) | Jadad total: 5 [Grade: A]; Schulz: Adequate | III |
| Onwude, 1995, UK: 14 wks parallel RCT233 | n-3 FA-enriched capsules: EPA 1.62 g/d DHA 1.08 g/d (n=113) | Control capsules: air-filled (n=119) | NS in birth wt & IUGR recurrence rate (grp 1 vs. grp 2) | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
| Olsen, 2000a, multicenter: 20 wks parallel RCT230 | Earl-PD: Pikasol (fish oil) 0.9g DHA, 1.3g EPA capsules (n=110) | Olive oil capsules (n=122) | (ITT) S↑ birth wt in fish oil NS % IUGR | Jadad total: 2 [Grade: C]; Schulz: Adequate | III |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
wt = weight;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
GA = gestational age;
IUGR = intrauterine growth retardation;
FA = fatty acids;
Scotland, Sweden, UK, Italy, Netherlands, Norway, Russia, Belgium
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker Correlations2,3 | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Smuts, 2003, US: 16 wks parallel RCT232 | n-3 FA-enriched eggs: DHA 0.23 g/d (n=18) | Control regular eggs (n=19)/ non-randomized low eggs grp (n=16) | Wt, length, & HC at birth ↑ in grp 1 vs. grp 2 (p-value: NR) rate of PD & LBW ↓ in grp 1 vs. grp 2 (p-value: NR) | n/a | Jadad total: 2 [Grade: C]; Schulz: Unclear | II |
| Smuts, 2003, US: 16 wks parallel RCT234 | n-3 FA-enriched eggs: DHA 0.23 g/d (n=142) | Control regular eggs (n=149) | NS in birth wt, birth length, HC, NS rate of LBW | n/a | Jadad total: 3 [Grade: B]; Schulz: Inadequate | II |
| de Groot, 2004, Netherlands: 26 wks parallel RCT196 | n-3 FA- enriched margarine: 25 g/d ALA 2.82 g/d LA 9.02 g/d (n=29) | Control margarine: 25 g/d ALA 0.03 g/d LA 10.94 g/d (n=29) | Birth wt S ↑ in ALA+LA vs. LA+ | S (+) correlation maternal plasma & RBC DHA & birth wt S +correlation DHA intake & bith wt | Jadad total: 3 [Grade: B]; Schulz: Unclear | III |
| Dunstan, 2004, Australia, UK: 20 wks parallel RCT231 | n-3 FA-enriched capsules: fish oil EPA 1.10 g/d DHA 2.20 g/d (n=40) | Control capsules: olive oil (n=43) | NS in length, wt, & HC at birth | n/a | Jadad total: 3 [Grade: B]; Schulz: Unclear | III |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
wt = weight;
RBC = red blood cells;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
GA = gestational age;
IUGR = intrauterine growth retardation;
FA = fatty acids;
PD = pre-term delivery (GA < 37 wks);
LBW = low birth weight;
HC = head circumference
Study characteristics. All but one study236, were double-blind parallel RCTs. The study by D'Almeida et al. was partially blinded.236 All the included studies were published in English scientific journals. Eleven trials had two arms; two studies included a third study group.209, 236 The trials had been conducted in the following countries: South Africa,236 Denmark,209 The Netherlands,196, 238 England,233, 235 Norway,141 the U.S.,232, 234 Australia and England.231 Olsen et al. conducted the three hospital-based trials in Denmark, Scotland, Sweden, England, Italy, The Netherlands, Norway, Russia, and Belgium.230 All but one study238 reported their funding sources: Enfamol Ltd.,236 Danish Medical Research Council, Sygekassernes Helsefond, Weiman's Legat & Michaelsen Fonden,209 Yorkshire Region Locally Organized Research, GLAXO (Leeds) and Seven Seas (Hull);233 Concerted Action and PECO programmes of the European Commission and the Danish National Research Foundation;230 Peter Moller Grants, Avd. Orkla ASA and “Aktieselskabet Chocololadefabrils Medicinske Fond;141 Scottish Office Health Department;235 Martek Biosciences Boulder Corporation (formerly OmegaTech, Inc.);232, 234 Unilever Research and Development (Vlaardingen, Netherlands);196 and, NH & MRC and Raine Medical Research Foundation (Australia).231
Population characteristics. The total number of enrolled pregnant women across the 10 trials was 3,404 and ranged from 60235 to 590141 participants. Helland et al. had a high rate of dropouts, leaving 341 women in the final analysis (57%).288
The age distribution of participants was reported in all but two trials.235, 238 The age of women across these studies ranged from 14236 to 40 years.233 Smuts et al. studied the youngest population of women with about 50% of participants aged between 16 and 21 years.234 Whereas, in the study by Bulstra-Ramakers et al., more than 50% of the women were between 20 and 29 years old.233 The age distribution across the study arms was not statistically different. However, in the Smuts et al. study,232 the experimental arm (omega-3 enriched eggs) consisted of significantly younger women than in the control arm (p <0.05).232
All but one study236 reported both inclusion and exclusion criteria. The 13 trials can be categorized into two groups—those trials investigating the effect of omega-3 dietary supplementation in pregnant women at risk of IUGR, due to a previous history of IUGR, twin pregnancy or history of premature delivery,230, 233, 238 and those trials that included only healthy pregnant women.141, 196, 209, 231, 232, 232, 234–236
The definition of a previous history of IUGR varied across the first group of studies. For example, Bulstra-Ramakers et al.238 defined IUGR as birth weight <10th PC, Onwude et al.233 defined it as birth weight <3rd PC, and Olsen et al.230 as a birth weight <5th PC.
In the second group of studies, women were relatively healthy except in the Dunstan et al. study,231 who reported that 40% and 58% of the women had asthma and allergic rhinitis, respectively. The second group of trials studied multiparous, as well as nulliparous women. The corresponding data on parity were reported in five of the 9 trials.141, 196, 209, 231, 234 The proportion of multiparous women across the studies ranged from 43%234 to 60%196 and with the exception of Smuts et al.'s study (42% vs 32%), were evenly distributed between the study arms.141, 196, 231
The trials excluded women with diabetes,230, 233–235, 238 gestational diabetes,232 systemic lupus erythematosus,234, 238 chronic hypertension,196, 233, 234 GHT,232, 235 placental abruption,209, 230, 233, 235 asthma,233 severe fetal malformation,141, 230 drug/alcohol abuse,230 regular intake of fish oil,196, 209, 230, 231 chronic illness (cardiovascular, cancer, renal, psychiatric, or neurological disorder),196, 232, 234 preeclampsia,232, 235 serious infectious disease (hepatitis),141, 234 serious bleeding episodes,209, 235 allergy to fish209, 235 or use of prostaglandin inhibitors.209, 235 Smuts et al. excluded women who had more than four pregnancies.232 Enrollment in one trial was restricted to non-smoking women.231 Malcolm et al also excluded twin pregnancies.235
Only three trials reported the racial composition of the study population.196, 232, 234 In two trials,232, 234 the majority of women were Black (81.0 and 73.2%, respectively). The third trial included only White women.196 There was no statistically different racial distribution between the study arms among these trials.
Ten studies reported on maternal tobacco smoking.141, 196, 209, 230, 231, 233, 234 The “Earl-IUGR” study by Olsen et al.230 had the highest prevalence of smokers (about 50%). In contrast, the lowest prevalence of smokers (about 19%) was in the study by Helland et al.141 In these trials, the arm-specific distributions of smokers were similar. In their trial, Dunstan et al. included only non-smokers.231
All trials reported the GA of the study participants at enrollment/intervention. In five trials,141, 232–234, 238 GA of women at the start of intervention ranged from 12 weeks238 to 32 weeks.233 For the remaining six trials, the lowest reported value of GA at intervention start was 16 weeks. The between-arm distribution of GA after randomization was reported as not different between-arms in nine trials.209, 230, 232–235
Only three trials reported on alcohol use,196, 231, 234 and in all of them, the distribution of alcohol users was similar between the randomized arms. The years of maternal education was reported in only two trials.141, 196
Intervention/exposure characteristics. In all 14 trials, the experimental intervention was the supplementation of the women's usual diet with omega-3 FA-enriched products. In 10 trials,209, 230, 231, 233, 235, 236, 238 the omega-3 FA supplementation was provided in capsules. The number of assigned capsules given to the women in these trials ranged from 4230 to 12 per day.238 In two trials,232, 234 women received omega-3 FA-enriched eggs. In 10 studies, the primary source of omega-3 FA supplementation was fish oil.141, 209, 230, 231, 233, 235, 236 In de Groot et al., the source of omega-3 FA supplementation was margarine.196 The experimental intervention in the majority of the trials consisted of the combined supplementation of DHA and EPA.141, 209, 230, 231, 233, 238 Participants in the de Groot et al. trial received dietary supplementation with ALA and LA.196 The supplementation provided to participants in the two Smuts et al. trials was eggs enriched with only DHA.232, 234 D'Almeida et al. used a mixture of evening primrose oil (GLA) and fish oil (DHA+EPA).236
The absolute amount of DHA ranged from 120233 to 135 mg per capsule (or per egg).232, 234 The study-defined daily dose (in grams) of DHA and EPA varied across the trials. The daily dose of DHA ranged from 0.20 g232 to 2.20 g.231 Whereas, the daily dose of EPA ranged from 0.80 g141 to 3.0 g.238 In the study by de Groot et al., the daily doses of ALA and LA were 2.8 g and 9 g, respectively.196
In most of the studies, intervention for the control group consisted of capsules,230, 233, 238 eggs,232, 234 or margarine196, with similar appearance and/or taste as those for the experimental intervention. The participants in the control arms received olive oil,209, 230, 231 coconut oil,238 or corn oil.141 Onwude et al.'s control group received airfilled capsules.233
The duration of the intervention was, in general, until delivery. The manufacturers of the omega-3 FA-enriched supplemental products were reported in 12 studies: R P Scherer Ltd. (UK);235 Enfamol Ltd.;236 Lube Ltd. (Denmark);209, 230 Peter Moller, Avd Orkla ASA (Norway);141 OmegaTech, Inc. (Bouldwer, CO)/Gold Circle Farms (U.S.);232, 234 Unilever Research and Development (Vlaardingen, Netherlands);196 and, Ocean Nutrition (Nova Scotia, Canada).231 Two trials did not report the names of the manufacturers.233, 238
The data on compliance (numbers of non-compliant participants and reasons for non-compliance) and type of analysis performed (i.e., ITT) were reported in six trials.209, 230, 233 Five studies used ITT analyses.230, 233 The numbers of non-compliant participants were reported in five studies.141, 196, 232, 234, 238 Dunstan et al. did not report well-documented compliance-related data.231
Cointervention characteristics. Six trials allowed 2 to 4 mg tocopherol/mL in the fish oil capsules.209, 230, 231 de Groot et al.'s margarines also contained vitamins (0.04%).196 In the Helland et al. study,141 the amount of fat-soluble vitamins was identical in the two oils provided to partipants (i.e., 117μg/mL of vitamin A, 1 μg/mL of vitamin D, and 1.4 mg/mL of tocopherol).
Five studies assessed the background diet of participants during the study.141, 209, 232, 235, 236 The studies used either a food-frequency questionnaire or a 24 hour recall questionnaire.236
Outcome characteristics. Of the 14 studies, three looked at the recurrence rate (i.e., percentage, relative risk, or odds ratio) of IUGR.230, 233, 238 Olsen et al., in the “Earl-IUGR” trial, evaluated the incidence of IUGR (not recurrence).230 Twelve trials measured and compared mean birth weight values (in grams) between the randomized arms, adjusted for GA and sex.141, 196, 209, 230–235 The rate of birth (i.e., percentage) of infants weighing <2,500 grams (LBW) was looked at in seven trials.230, 232, 234, 236, 238 The infants' birth length and HC (in cm) between the randomized groups were compared in five trials.141, 231, 232, 234, 235
| Study Quality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| A | B | C | ||||||||
| Applicability | I | Author | Year | n | Author | Year | n | Author | Year | n |
| II | Author | Year | n | Author | Year | n | Author | Year | n | |
| OnwudeA | 1995 | 233 | SmutsI | 2003 | 250 | SmutsU | 2003 | 73 | ||
| HellandU | 2001 | 590 | MalcolmU | 2003 | 100 | |||||
| III | Author | Year | n | Author | Year | n | Author | Year | n | |
| Bulstra-RamakersA | 1994 | 68 | DunstanU | 2004 | 98 | OlsenI | 1992 | 533 | ||
| de GrootU | 2004 | 79 | D'AlmeidaI | 1992 | 150 | |||||
| OlsenA | 2000 | 232* | ||||||||
| OlsenA | 2000 | 280** | ||||||||
| OlsenA | 2000 | 579*** | ||||||||
| OlsenA | 2000 | 63^ | ||||||||
n = number of allocated/selected participants;
RCT = Adequate vs UUnclear allocation concealment; I Inadequate
“Earl-PD” trial;
“Earl-IUGR” trial;
“Twins” trial;
“Susp-IUGR” trial
The three studies investigating the effect of omega-3 FA dietary supplementation on pregnant women with a previous history of IUGR, concluded that the randomized groups did not differ with respect to the recurrence of IUGR (birth weight < 3rd and 10th PC adjusted for GA).230, 233, 238
The between-group difference in the mean birth weight was not significantly different in eight of 12 studies.141, 209, 230, 231, 233–235 However, in three trials, the mean birth weight was significantly higher in the omega-3 FA-supplemented group compared with the group without supplementation.196, 230, 232 In contrast, the “Earl-IUGR” trial found a significantly higher mean birth weight in the olive oil group compared with the fish oil group.230
Regarding birth length, three studies did not find a statistical difference between study arms.141, 231, 235 On the other hand, in the Smuts et al. trial, infants in the high-DHA egg group had a significantly higher birth length compared with those in the ordinary egg group.234 HC at birth was similar in both groups across four trials.141, 231, 234, 235
Results of five trials showed that omega-3 FA supplementation did not influence the incidence rate of LBW infants from pregnant women with or without a history of previous IUGR.230, 234, 238 In the trial conducted by Smuts et al., no LBW infants were born to women receiving omega-3 FA supplementation, and the incidence rate of LBW infants born to women in the control arm was 26%.232 In D'Almeida et al., the percentage of infants born weighing <2,000 g was noticeable lower in the omega-3 FA supplemented group compared with the other two groups (placebo: 3.3%, magnesium: 4.7%, fish oil+primrose oil: 1.4%); however, no p-value was reported.
Only one study evaluated the association between maternal biomarkers with this clinical outcome.196 de Groot et al. found a positive correlation between maternal plasma and RBC DHA and birth weight, when controlled for birth order. This difference was nonsignificant at delivery. There was also a statistically positive correlation between the total estimated DHA intake and birth weight. However, this study provided ALA and LA as supplementation.196
Seven studies reported data on dropouts/withdrawals, albeit with different detail.141, 196, 209, 231, 234, 235, 238 The most frequent reasons for study drop-out were: discomfort in consuming fish oil or margarine; lack of compliance; refusal to participate because it was time consuming; morning sickness; and/or, nausea. The number of non-completers across the trials ranged from 1233 to 57.234
After examining the studies for source of oil and duration of supplementation, seven trials209, 230, 231, 233, 238 were initially considered for meta-analysis. For Olsen et al. data from only three of six trials was considered (DHA+EPA vs. control): prophylactic EARL-IUGR trial, therapeutic Susp-IUGR trial, and prophylactic Twins trial.230 Olsen et al.209 and Dunstan et al.231 were carried in a healthy population (i.e. women without previous history of high risk pregnancy). Thus five trials230, 233, 238 were considered for meta-analysis.
For the birth weight outcome, data from the Susp-IUGR trial230 could not be included since it was reported as birth weight adjusted for GA, unlike the other studies. Bustra-Ramakers et al.238 did not report birth weight. Thus three trials230, 233 were available for meta-analysis.
For the intra-uterine growth retardation (IUGR) outcome, the therapeutic trial Susp-IUGR230 could not be included since it did not report IUGR outcomes. Thus four trials230, 233, 238 were available for meta-analysis.
Meta-analysis was performed using the random effects weighted mean difference. For the Onwude et al. study'233 the standard deviations in the two study groups were not reported, however, a 95% confidence interval for the difference in means was reported. We assumed the standard deviations were the same in both groups, and computed the standard deviation from the confidence interval.
In two studies,230, 233 the overall size of the effect in the mean birth weight did not reach statistical significance (weight mean difference: -61.51, CI 95%: -256.21; 133.18).
Meta-analysis was performed using a random-effects model for odds ratios.
In three studies,230, 233, 238 the overall size of the effect on the incidence of IUGR between DHA+EPA and control groups was nonstatistically significant (OR: 1.14, CI 95%: 0.79; 1.64).
The observed between-group differences in birth weight in three studies,209, 230, 232 were adjusted for potential effect modifiers (i.e., duration of pregnancy, infant's gender, placental weight, maternal age, other characteristics).
Linear regression analysis revealed that the duration of pregnancy was an important predictor (potential confounder) of birth weight.230 The higher birth weight observed in the experimental group compared with the control group was partially due to the effect of duration of pregnancy, which was not evenly distributed between the randomized groups. Once this difference was accounted for, by adjusting for duration of pregnancy, the earlier observed difference in birth weight was attenuated.230 In another study,232 using ANOVA, it was found that birth order was an important predictor of birth weight and length. Smuts et al. used a multiple linear regression to account for effect modifiers by adjusting the effects of interest for race, the number of prior pregnancies, previous premature deliveries, smoking, maternal body mass index (BMI), age, alcohol use, and maternal RBC-DHA levels.234
In the study of Smuts et al., women randomized to receive the diet supplemented with omega-3 FAs (DHA-enriched eggs) were substantially younger compared with those women receiving the diet without this supplementation (regular eggs) (mean age: 19.9 vs 24.8 year, p <0.05).232 The authors did not report any attempt to adjust for the effect of age.
In de Groot et al.,196 the observed difference in birth weight was adjusted for the duration of pregnancy. In their “Susp-IUGR” trial, Olsen et al. found that the mean birth weight adjusted for GA at delivery did not differ between the two randomized groups.230
The analysis revealed that the effect estimates for birth weight, length, and HC were strongly influenced by maternal BMI, race, smoking status, and number of pregnancies. The adjustment for the above-mentioned covariates attenuated the earlier observed crude differences in birth weight, length, and HC. In de Groot et al., duration of pregnancy was an influential covariate for the association between the allocation to the experimental intervention and birth weight.196
In two studies,232, 238 the randomized groups were not balanced with respect to the important prognostic/predictive factors such as GHT238 and age.232
None of the studies adjusted the outcomes results for the maternal background diet.
The power calculation was reported in seven trials,31, 288, 292, 296 while the intention-to-treat analysis approach was reported in four trials.31
| Author, Year, Location: Design | Study groups1 | Notable associations2,3 | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Reece, 1997, US: Case-control study239 | Preterm births (n=37) | Term deliveries controls (n=34) | Maternal RBC LA, AA, DHA S ↑ in preterm vs. 34-wk control+ & term+++ | Quality score: 4 [Grade C] | III |
| Maternal RBC EPA S ↑in term controls vs. both preterm & 34-wk control++ | |||||
| Maternal RBC & plasma n-3/n-6 ratio was S↑ in term controls vs. preterm++ | |||||
| NS Maternal RBC n-3/n6 between preterm & 34-wk control | |||||
| Maternal plasma LA S ↑ in preterm & 34-wk control vs. term control+ | |||||
| Maternal plasma LA, AA, EPA S↑ in preterm vs. term controls+ | |||||
| Elias, 2001, Canada: Single prospective cohort240 | Healthy pregnant women (n=84) | n/a | Umbilical cord plasma TGL & CE AA S (+) associated with GA++ | Quality score: 6 [Grade B] | III |
| NS association between other maternal n-3 or n-6 BMK & GA | |||||
| Maternal plasma TGL AA S (+) correlated to GA++ | |||||
| Rump, 2001, Netherlands: Cross-sectional241 | Healthy pregnant women-term infants (n=627) | n/a | NS correlation between maternal plasma FA at 11 (8) wk GA & at delivery & GA | Quality score: 9 [Grade A] | III |
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
LA = linoleic acid;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
N/A = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
BMK = biomarker;
RBC = red blood cells;
PL = phospholipid;
CE = cholesteryl ester;
TGL = triacylglycerol;
GA = gestational age/duration of gestation;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
↑ = increase;
↓ = decrease/reduction
Reece et al. compared blood LCPUFA content of 37 mother-infant pairs with preterm delivery (mean GA 34 weeks) with a group of 34 control full-term mother-infant pairs (mean GA 40 weeks).239 The study was conducted in the U.S. and was supported by the Colorado Agricultural Experiment Station. The study included a sample of preterm and term cases based on the duration of gestation.239 “Preterm delivery” (n=37) was defined as GA of less than 37 weeks, whereas, “term delivery” (n=34) was defined as GA of 37 or more weeks. The patients were excluded if they had a recognized cause of preterm birth (i.e., uterine abnormality, intrauterine infection, substance abuse, multiple gestation, pregnancy-onset hypertension). Exclusions for controls included recognized medical problems, multiple gestations, multiple parity, GHT, and substance abuse.239 Participants were enrolled at 18 weeks of GA and followed until delivery.239
In preterm cases, the maternal blood samples were obtained at delivery, while the control women were sampled at 34 weeks of GA and at delivery.239
The cases were well-matched with the controls in terms of marital status (50% married), race (82% white), financial support (80% public), pre-pregnancy body mass index, maternal infection detected (70% none), type of labor and maternal age.239 Both populations significantly differed in the duration of gestation (mean GA: 40.2 [SD=0.2] weeks vs 33.9 [SD=0.6] weeks), birth weight, length and HC (preterm infants had significantly lower growth parameters at birth than term infants).239
Reece et al. found that the RBC FA content (% total) of LA (omega-6), AA, and DHA was significantly higher in the preterm cases compared with the controls at 34 weeks GA and at term.239 The percent total EPA in RBC in controls at term was significantly higher than both preterm deliveries and 34-week controls. The maternal RBC omega-3/omega-6 ratio content was significantly higher in control term deliveries compared with preterm cases. The maternal plasma percent total LA (omega-6) was significantly increased in the 34-week control and preterm groups compared with the term control group. The plasma percent total LA, AA, EPA was significantly higher in preterm cases compared with term controls. The plasma AA content was increased in 70% of preterm cases compared with control cases at term.239
Elias and Innis determined the association between length of gestation and the maternal plasma concentration of AA and DHA in a cohort of pregnant women (n=84) at 35 weeks of GA.240 The study was conducted in Canada and was supported by the Molly Towell Perinatal Research Foundation and the National Science and Engineering Research Council of Canada.240 The cohort included 60 women at 22 to 24 weeks of GA that were recruited from predelivery registration records and were followed until delivery. An additional 24 pregnant women were recruited from a low-risk delivery unit in Canada. Women with a history of surgical or medical problems that could influence the lipid metabolism or fetal growth were excluded from the study. These included women with more than one fetus, hyperemesis, psychological or social problems, illicit drug or alcohol use, cardiac or renal disease, diabetes, epilepsy, respiratory or rheumatoid conditions, cholestasis, high cholesterol or triglycerides before pregnancy, HIV infection, hepatitis, or tuberculosis.240
The study measured the maternal intake, during pregnancy, of the different FAs through a food-frequency questionnaire designed to collect data on amounts and sources of fat, methods of food preparation, brand names and places of food purchase.240
The outcome measures were the maternal blood content of omega-3 and/or omega-6 FA during pregnancy and its relationship with the duration of gestation, as well as the infant FA blood content.240
Ellis and Innis did not find a significant association between the maternal plasma content of omega-3 and omega-6 FA and the duration of gestation, except for the maternal plasma triglyceride (TGL) AA content that was positively related to the length of gestation. However, this uncontrolled study did not provide the details regarding this association, as well as the fact that all the pregnancies reached term.240
Rump et al. was a cross-sectional study that included a sample of healthy pregnant woman and their term infants.241 It was conducted in the Netherlands and supported by a Hospital, and Nutricia Research. The blood samples were taken at 16 weeks and after delivery.241
The cohort was separated by weight for gestational age groups, SGA (PC <10th), AGA (PC >10th and <90th) and LGA (PC >90th). The groups were comaparable in terms of maternal characteristics like age, height, weight, parity, smoking status, and mode of delivery.241
There was no correlation between the maternal content of PUFA and the birth weight.241
Study quality and applicability. Although they employed different research designs, all the studies were assigned a level III for applicability, and together they received a mean quality score of 6.3.
| Author, Year, Location: Design | Study groups1 | Notable associations2,3 | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Wang, 1991, US: Cross sectional study242 | Preeclampsia (n=9)/ | normal pregnant pts(n=11)/ nonpregnant women volunteers (n=10) | Total PUFA, LA (n-6), ALA (n-3) & EPA plasma of normal pregnant women was S > preeclamptic pts+ | Quality score: 5 [Grade B] | III |
| NS between groups plasma AA & DHA | |||||
| S > EPA & DHA in normal pregnant women vs. nonpregnant++ | |||||
| Craig-Schmidt, 1994, US: Cross-sectional study243 | preeclampsia (n=10)/ normal pregnancy (n=10) | GHT (n=10)/ CHT (n=6) | NS among groups in plasma saturated, monosaturated & PUFAs | Quality score: 2 [Grade C] | III |
| NS in n-6 or n-3 FA between normal pregnancies & GHT, preeclamsia or CHT | |||||
| CHT S ↑ AA in plasma PL vs. other groups | |||||
| NS in plasma PL EPA among the groups | |||||
| NS in AA/EPA ratio & n-6/n-3 ratio | |||||
| Al, 1995, Netherlands:nested case-control study179 | GHT women (n=52) | Healthy pregnant controls (n=156) | NS in absolute FA composition (mg/L) of maternal plasma PL (before 16, at 22 & 32 wks GA) | Quality score: 11 [Grade A] | III |
| Severe GHT women (n=17) mean GA & mean birth wt of their babies S ↓ than mild GHT | |||||
| During gestation & after delivery NS in maternal FA composition of the severe GHT vs. mild GHT | |||||
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
E-EPA = ethyl eicosapentaenoate;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
grp = group;
wk = week(s);
mo = month;
PL = phospholipid;
CPG = choline phosphoglycerides;
EPG = ethanolamine phosphoglycerides;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
GHT = gestational hypertension;
PL = phospholipids;
CHT = chronic hypertension
| Author, Year, Location: Length & Design | Study groups1 | Notable associations2,3 | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Hofmann, 1998, Germany: Cross-sectional study229 | Preeclampsia (n=14) | Healthy pregnant controls (n=16) | Total FA in plasma TGL during pregnancy were S > in preeclamptic group vs. control+++ | Quality score: 6 [Grade B] | III |
| NS between groups in AA plasma TGL during pregnancy | |||||
| LA (n-6) & DHA (n-3) content in plasma TGL were S ↓ in preeclamptic pts vs. controls+ | |||||
| NS between groups LA & AA (n-6) in plasma PL | |||||
| DHA plasma PL content was S ↓ in preeclamptic women++ | |||||
| Shouk, 1999, Egypt: Cross-sectional study244 | severe preeclampsia in 3rd trimester (n=25) | healthy pregnant controls (n=20) | AA in plasma was S > in preeclamptic women vs. control+++ | Quality score: 7 [Grade B] | III |
| NS between groups LA & ALA (n-3) content | |||||
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
E-EPA = ethyl eicosapentaenoate;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
PL = phospholipid;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
TGL = triglycerides
Four studies had a cross-sectional design,229, 242–244 whereas, one was a nested case-control study derived from a prospective cohort.179
Study characteristics. Of the five observational studies that met eligibility criteria, two studies were conducted in the U.S.,242, 243 one was conducted in The Netherlands179, one in Germany229 and one in Egypt.244 Two studies compared the outcomes in more than two groups,242, 243 whereas, three studies involved only three arms.179, 229, 244
Most studies were published in scientific journals in English, but one required translation from German.229 The funding source was reported in two of five studies. Wang et al. was supported by a pharmaceutical industry (Glaxo, Inc.),242 whereas, Al et al. was funded by Nutricia BV, Zoetermeer, The Netherlands.179
Population characteristics. There were 349 subjects included across the studies. The sample sizes ranged from 30 to 208 patients. Three studies reported the inclusion and exclusion criteria.179, 229, 244
Wang et al. selected three groups of women between 20 and 40 years, normal pregnant patients (n=11), preeclamptic patients (n=9) and nonpregnant female volunteers as controls. All were at term.242 Craig-Schmidt et al. included nulliparous pregnant women (mean age: 21 [SD=6] years).243 The study groups were composed of women with normal pregnancy (n=10), GHT (n=10), preeclampsia (n=10), and chronic hypertension (n=6).243
Al et al. selected, from the prospective cohort of healthy pregnant women (GA <16 wks), a group of women with GHT and matched them with a group of healthy pregnant patients.179 Hofmann et al.229 and Shouk et al.244 compared a group of women with preeclampsia with a healthy pregnant control group, although Shouk et al.'s patients had a severe preeclamsia in the third trimester.
Shouk et al. did not provide a definition for preeclampsia.244 In general, preeclampsia was defined as as BP greater than 140/90 mm Hg measured on two occasions, 6 hours apart starting from the 20th week of GA. Proteinuria was defined as greater than 300 mg urinary protein per 24 h; preeclampsia was the combination of hypertension and proteinuria with or without edema.179, 229, 242, 243
Wang et al.242 and Craig-Schmidt et al.243 failed to provide information about the between-group difference in terms of population characteristics (i.e., maternal age, GA, parity, education, smoking status, etc.) at baseline or before the study. Al et al. did not find a significant difference between groups in maternal age, number of nulliparous women, percentage of smoking women, or number of infants small for gestational age (SGA) at term.179 There was a significant difference between groups in diastolic BP at entry (GHT higher than control), maximum diastolic BP (GHT >control), GA at delivery (GHT < control), birth weight (GHT < control), and APGAR score at 5 min (GHT < control).179 Control of selection bias was achieved by measuring the FA content of pregnant women (at 16 weeks GA) who decided not to participate in the trial.179
Hofmann et al.'s study groups were well-matched for maternal age, BMI, GA, serum creatinine, blood glucose and hematocrit. Blood pressure was significantly higher in the preeclamptic women.229 Similarly, Shouk et al.'s patients were well-matched for age, parity and GA.244
Regarding the medications and/or treatments allowed before study entry, Wang et al.242 and Hofmann et al.'s229 preeclamptic women did not receive aspirin. The rest of the studies did not report the use of medication in their patients.
Hofmann et al. and Shouk et al. included patients without other comorbid conditions.229, 244 The remainig three studies did not provide this information.179, 242, 243
Intervention/exposure characteristics. Groups in the study by Al et al. did not differ in their nutrient intake during pregnancy.179 None of the identified studies described the nature of the nutritional intake, including the use of supplements or any other substance that could alter the lipid content in maternal blood biomarkers.
Outcome characteristics. All studies examined the omega-3 and omega-6 FA content in plasma of maternal blood from preeclamptic women compared with healthy controls.
Study quality and applicability. The total quality score across the studies was 6.2, however the applicability level was III.
Wang et al. found that the total PUFA, LA (omega-6), ALA (omega-3) and EPA content in plasma (mg/L, mean) of normal pregnant women was significantly higher than in the preeclamptic patients.242 There was a nonsignificant difference between groups in the content of AA and DHA in plasma. However, there was a significantly higher content of EPA and DHA in normal pregnant women compared with nonpregnant.242
Craig-Schmidt et al. did not observe a significant difference between groups in saturated, monosaturated and PUFAs, or in the content of omega-6 or omega-3 FA (mg/L and % of total FA) between women with normal pregnancies and women with GHT, preeclamsia or chronic hypertension.243 The women with chronic hypertension had a significantly greater AA in plasma phospholipid compared with the other three groups. There was a nonsignificant difference in plasma phospholipid EPA concentrations among the groups, as well as in the AA/EPA ratio or omega-6/omega-3 ratio at baseline.243
During pregnancy (before 16, at 22 and 32 weeks GA) no significant differences in the absolute FA composition (mg/L and % total FA) of maternal plasma phospholipid were observed between groups in the Al et al. study.179 After delivery, however, the amount of ALA (omega-3) was significantly lower in the GHT women compared with women who had normal pregnancies. After correction for differences in GA between groups, significantly higher levels of DHA were observed in umbilical plasma of the GHT compared with controls.179 When the GHT women were stratified by severity of hypertension, patients with severe GHT (diatolic BP >105 mmHg) (n=17), 12 of which had proteinuria, had a mean GA and mean infant birth weight that were significantly lower than those in the group with mild GHT (diastolic BP <105 mmHg). During gestation and after delivery, no significant differences were observed in the maternal FA composition of women with severe GHT compared with those with mild GHT.179
Hofmann et al. found that the total amount of FA in plasma triglycerides during pregnancy were significantly higher in the preeclamptic group compared with the healthy control group. The difference disappeared on the 5th day after delivery.229 The AA content in plasma triglycerides did not differ between groups during pregnancy. On the other hand, the LA (omega-6) and DHA (omega-3) content in this blood fraction were significantly lower in the preeclamptic women compared with the controls. The LA and AA (omega-6) concentration in plasma phospholipid were not significantly different between groups, however, the DHA plasma phospholipid content was significantly lower in preeclamptic women.229
Shouk et al. observed that the AA in plasma (mcg/L) was significantly higher in preeclamptic women. LA and ALA (omega-3) content did not differ between groups.244
| Author, Year, Location: Design | Study groups1 | Notable associations2,3 | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Vilbergson, 1991, Sweden: Cross-sectional247 | SGA grp (n=13) | Term AGA (control) (n=20) | S↓ maternal plasma DHA & AA in SGA grp than in ctrl at 34 weeks GA & at delivery+ | Quality score: 7 [Grade B] | III |
| Matorras, 1994, Spain: Case-control245 | IUGR grp (n=23) | AGA (control) (n=34) | S↑ maternal plasma EPA in IUGR grp than in ctrl at delivery++ | Quality score: 9 [Grade A] | III |
| NS in maternal plasma DHA & AA at delivery | |||||
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
AGA = appropriate for gestational age;
IUGR = intrauterine growth restriction;
GA = gestational age;
ct = control group;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
BW = birth weight;
Fas = fatty acids;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
grp = group;
wk = week(s);
mo = month;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
SGA = small for gestational age;
AGA = adequate for gestational age;
IUGR = intrauterine growth retardation
| Author, Year, Location: Design | Study groups1 | Notable associations2,3 | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Elias, 2001, Canada: Single prospective cohort240 | Healthy pregnant women (n=84) | n/a | Maternal plasma TGL AA, S (+) correlated to infant birth wt & length++ | Quality score: 6 [Grade B] | III |
| Rump, 2001, Netherlands: Cross-sectional241 | Healthy pregnant women-term infants (n=627) | n/a | NS relation between maternal plasma FA at 11 (8) wk GA & at delivery & infants BW | Quality score: 9 [Grade A] | III |
| Cetin, 2002, Italy: Case-control246 | IUGR grp (n=10) | AGA (control) (n=11) | S↑ maternal plasma EPA in IUGR grp than in pb at ≈28.2(8.0) wk GA+ | Quality score: 5 [Grade B] | III |
| NS in maternal plasma DHA & AA at ≈28.2 (8.0) wk GA | |||||
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
GA = gestational age;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
BW = birth weight;
TGL = triacylglycerol;
FAs = fatty acids;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
grp = group;
wk = week(s);
mo = month;
wt = weight;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
SGA = small for gestational age;
LGA = large for gestational age
Matorras et al., in a case-control intrapartum study, analyzed the relationship between maternal plasma LCPUFAs and IUGR in an apparently well-nourished population of pregnant women in the second stage of labor.245
Study characteristics. The studies were conducted in different countries, including one from Canada,240 and one each from Sweden,247 Spain,245 Italy246 and The Netherlands.241 Four studies reported their funding sources and these included a professional society, university and foundation,240, 247 and government.240, 245, 246
Population characteristics. Four studies selected a small number of participants, ranging from 21246 to 84.240 Only Rump et al. studied a large sample of infants (n=81 SGA, n=505 AGA, n=41 LGA).241
Four studies presented clearly-defined inclusion and exclusion criteria240, 241, 245, 247 and one study exclusively described exclusion criteria.246 Vilbergsson et al. included only singleton pregnancies and made an effort to equally distribute subjects to groups by age, parity, and dietary intake; maternal diabetes was an exclusion criterion.247 Matorras et al. included term SGA infants with no malformations and chromosomal abnormalities, delivered from a singleton pregnancy, with an accordance between GA (determined by last menstrual period and early ultrasound) and pediatric evaluation using the Dubowitz test.245 Elias and Innis included healthy pregnant women (GA 22–24 weeks), whereas, women with medical or surgical problems that could influence lipid metabolism were not eligible.240 In the study of Rump et al., selection criteria for inclusion/exclusion were GA <16 weeks at entry, diastolic BP <90 mmHg and no signs of cardiovascular, neurologic, renal, or metabolic disorders at the time of recruitment.241 Cetin et al. set the following exclusion criteria for both normal and IUGR pregnancies: subsequent development of gestational diabetes or GHT; abnormal fetus caryotype; or, malformation at birth.246
The mean GA was reported in all of the five studies. The mean GA for the entire SGA group of infants ranged from 36247 to 40.6 weeks.241 Statistically significant differences in GA between the SGA/IUGR and AGA groups were reported in two studies.246, 247 In the remaining three studies, the SGA/IUGR cohort and AGA controls were of similar age at birth.241, 245, 246
Definition of IUGR and/or SGA was given in four studies.241, 245–247 Cetin et al.246 and Matorras et al.245 established IUGR by performing ultrasonographic examination measuring fetal biparietal diameter and/or abdominal circumference, which had to be under the 10th PC of reference values for fetuses of a similar age. In the study of Cetin et al., growth retardation was confirmed at birth if the neonatal weight was below the 10th PC according to standards for birth and weight and GA.246 Rump et al.241 classified infants as SGA if their birth weight was ≤10th PC of reference values, whereas Vilbergsson et al.247 defined SGA as an infant birth weight two standard deviations below the mean when compared with a standard growth chart.
No authors explicitly stated the racial/ethnic background of the study participants, yet it is likely that Caucasian/Europeans were represented as a majority in all of these studies.
Information regarding maternal smoking history and/or smoking during pregnancy was available in two studies and even though there was a higher proportion of smokers in the SGA/IUGR group than in control group, the difference did not reach statistical significance.241, 245 Vilbergsson et al reported that the control group contained no smokers and in the group at risk for IUGR, there were no differences between smokers and nonsmokers with respect to clinical characteristics or FAs results.247 Alcohol consumption during pregnancy was not reported in any of the five studies.
None of the studies reported the use of medication and/or supplements before study entry or any comorbid conditions in newborn babies. Maternal characteristics such as parity, and age, height, weight at study entry, were similar between study groups in three studies.241, 246, 247 However, in the study of Matorras et al.,245 IUGR mothers had lower height, pregestational weight and weight increase during pregnancy than mothers in the control group.
Only one study reported the mean maternal energy intake during pregnancy, which was similar between control and IUGR groups.245 The same study evaluated socioeconomic levels of study population and reported that twice as many women with IUGR pregnancies belonged to low socioeconomic strata. The description of lipid extraction and biochemical analysis was adequate in all but one study.247
Outcome characteristics. The main outcome evaluated in these observational studies was incidence of births of SGA infants and its relation to either the absolute or relative amount of maternal plasma FA concentrations during pregnancy. Information regarding the timing of the maternal plasma LCPUFA analysis was reported in all but one study.247
In the study of Vilbergsson et al., maternal blood samples were drawn in the 34th and 37th week of pregnancy, at delivery, and at 4 days postpartum. This study measured the plasma content in phospholipids (lecitin) of LCPUFA (mol %).247 Cetin et al. reported that maternal sample collection and analysis were done at 28.2±8.0 weeks GA in the AGA control group and at 28.6±4.3 weeks GA in IUGR group. The plasma PUFA were measured in mcg/ml and % weight of total FA.246 In the study of Rump et al., maternal venous blood samples were collected at 11±3 weeks GA. The plasma FA were measured in % weight of total FA.241 Matorras et al. obtained maternal blood samples during the second stage of labor. The plasma FA were measured in % weight of total FA 245 The correlation between maternal plasma FA composition and the main outcomes was calculated using Pearson's correlation coefficient, following the standard criteria of applicability,245 linear regression analysis,246 and simple and multiple regression models.241, 247 Elias and Innis assessed the association between maternal plasma PUFA and the birth weight and length of infants. The plasma FA were measured in % weight of total FA.240
Study quality and applicability. Although they employed different research designs, all the studies were assigned a level of applicability of III and together, received a mean quality score of 7.2.
Vibergsson et al.247 found that in a subgroup of SGA participants, maternal plasma DHA and AA concentrations were significantly lower than those in a control group at 34 weeks GA as well as at delivery. The study results of both Matorras et al.245 and Cetin et al.246 were similar. In the Spanish case-control study, Matorras et al. revealed that maternal plasma EPA concentrations expressed in percentage values of total amount of plasma FAs, were significantly increased in IUGR mothers compared with controls at delivery.245 Conversely, there were no differences in percentage values nor in absolute values in the other FAs analyzed in newborn infants.245 Cetin et al. observed significantly higher maternal plasma EPA in the IUGR group compared with the normal control group in the third trimester of pregnancy.246
Rump et al. found that observed changes in maternal plasma LCPUFA concentrations (% wt FA) were related to the size of the infants.241 Significantly bigger decreases in plasma concentrations of AA and DHA were noted in mothers of AGA control infants compared with mothers of the SGA group, whereas, the largest reduction in the fraction of linoleic acid was found in the mothers of SGA infants. No cross-sectional association was found between maternal FA concentrations and infant size at birth at study entry or at delivery, as well as between maternal plasma FA concentrations and the total duration of gestation.
Elias and Innis observed that the maternal plasma TGL AA, but not phospholipid or cholesteryl ester AA, was positively related to infant birth weight and length (p<0.01). No other correlations were found between maternal plasma omega-3 or omega-6 FAs and these variables.240
| Author, Year, Location: Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Helland, 2001, Norway: 34 wks parallel RCT141 | Cod liver oil (DHA+AA+EPA) (n=301 mothers; n=175 infants) | Corn oil (LA+ALA) (n=289 mothers; n=166 infants) | NS between groups in weight, length & head circumference at any point | Jadad total: 4 [Grade: A]; Schulz: Unclear | III |
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
E-EPA = ethyl eicosapentaenoate;
n = sample size;
pts = study participants;
NR = not reported;
NS = nonsignificant statistical difference;
N/A = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
RBC = red blood cells;
PL = phospholipid;
p<.05 or significant with 95% confidence interval;
++p<.01;
+++p<.001;
++++p<.0001;
↑ = increase;
↓ = decrease/reduction
Helland et al.,141 has been described in detail in the Pregnancy Outcomes section. A summary and the results relating to the current question are discussed here.
Helland et al. assessed the gestational length, birth weight, and neurologic and cognitive outcomes in a sample of infants born of healthy pregnant women. Participants were randomized to receive either cod liver oil (1,183 mg/10 mL DHA, 803 mg EPA, 27.5 mg AA) or corn oil (LA and ALA) from week 18 of pregnancy to 3 months post delivery.141
The participants (n=590 enrolled) were included if they were healthy, with single pregnancies, between 19 and 35 years of age, and intended to breastfeed their infant. They should not have taken any supplements of omega-3 FA earlier in the pregnancy. The exclusion criteria were premature births, birth asphyxia, infections, and anomalies in the infants that required special attention.141 Infant growth patterns (i.e., weight, length and HC) were measured at birth, 6 weeks and 3, 6, 9 and 12 months. Helland et al. had a high rate of dropouts, leaving 341 women in the final analysis (57%).288
The groups did not differ significantly in weight, length and HC at any time point during the study.141
No correlation was found between these parameters and infant plasma biomarkers.
Study quality and applicability. The Jadad total quality score was 4 (did not report double-blinding method) and the allocation concealment was unclear in the report. The applicability level was III.
Jensen et al. investigated the effect of DHA supplementation in lactating women on the visual function and growth of their infants.248 Mothers were assigned randomily to receive 200 to 250 mg DHA per day as either algal DHA (n=42), refined high-DHA fish oil (n=42) or placebo (n=42), for 120 days after delivery. Infant characteristics, as well as maternal characteristics, were not described in this abstract.248 The study showed no differences between the three diet groups in the weight, length or HC of the infants at 120 and 240 days.248
Xiang et al. evaluated the growth patterns in a random sample of healthy mother-term infant pairs (n=19) at 1 and 3 months of age. The infants were exclusively breastfed during the study period.249 Rocquelin et al. investigated the role of human milk LCPUFAs in term infant growth in two African suburban random samples of nursing mothers and their 5 month old infants.302
Xiang et al. was conducted in Sweden and was supported by the Wenner-Gren Centre Foundation.249 Rocquelin et al. was conducted in in The Congo and Burkina Faso (Africa), and supported partly by the Institut National de la Recherceh Agronomique.302
Xiang et al. did not report the inclusion and exclusion criteria, yet described the included sample as mother-infant pairs without acute or chronic conditions. The infants were exclusively breastfed during the 3 months of the study. The mothers registered the total intake of food and fluid, and a 3-day dietary record was obtained; however, the LCPUFA content was not measured. The maternal milk FA composition was measured at each visit.249
Rocquelin et al. conducted a survey in two random samples of nursing mothers and their 5-month old infants born at term—102 participants in Congo and 101 in Burkina Faso.302 The report failed to describe the inclusion and exclusion criteria. The dietary habits of the mothers was established using a Food-frequency questionnaire. The outcomes measured were the growth patterns (weight and height from birth to 5 months of age).302 The maternal age, height, BMI, and maternal occupation did not differ significantly between both locations, however, maternal education was significantly superior in participants in Congo compared with those in Burkina Faso. The characteristics of the participants' homes (i.e., electricity, refrigerator, private water supply, private toilets, radio set, TV set) were significantly different between cities.302
The feeding practices of the mothers were measured in each location. None of the infants were exclusively breastfed. All the infants in Burkina Faso were receiving extra fluids (e.g. water or juice) compared with 51% of Congo infants. However, the Burkina Faso infants had a significantly higher proportion of predominance of breast feeding and exclusion of solid foods. The LCPUFA content in breast milk and foods given to the infants were measured at both sites. The breast milk fat content was slightly lower in mothers in Congo. The content of omega-6 FA in the human milk of women in Burkina Faso was significantly higher than in Congo, yet it provided significantly lower (half) concentrations of omega-3 FA. Consequently, the LA omega-6/ALA omega-3 ratio and the LC omega-6/LC omega-3 ratio were 4.3 and 4.5 times higher, respectively, in Burkina Faso than in Congo.
The fat and PUFA concentrations in flours fed as gruels were predominantly from corn and millet. In Burkina Faso, infants also received commercial infant formula (Cerelac) containing LA (800 mg/100g), ALA (29 mg/100g) (i.e., LA/ALA=28.0). In Congo, the FA content was LA 1,080 mg/100g, ALA 73 g/100g (i.e., LA/ALA=14.8).302
In the Xiang et al. study, the LC PUFAs fraction (13.5% of total FA) in human milk (LA and ALA) increased significantly during the 3 months of lactation, whereas, DHA decreased significantly but not the EPA maternal milk content.249 The ratio of AA to DHA in the mother's milk correlated positively with the infants' rate of increase of HC at 1 month and 3 months of age, as well as with the gain in estimated brain weight at 1 and 3 months of age. No relations were found between HC or estimated brain weight and LA, ALA, AA or DHA content in human milk.249
Infants in Rocquelin et al.'s study did not differ in gender, percentage of LBW (<2,500 g), birth weight or length, between the two sites.302 However, the infants in Congo were significantly younger than in Burkina Faso. The weight-for-age and weight-for height z-scores and weight gain (in grams) were significantly lower in infants in Burkina Faso than in those in Congo.
When comparing the anthropometric data (birth weight, age, weight gain) of predominantly breastfed to complementary fed infants in Burkina Faso, no differences between groups were detected. Since both populations were extremely different, the analysis of the relationship between the FA content in breast milk and anthropometric data between cities was excluded from the review.302
Study quality and applicability. Jensen et al. was not assessed by Jadad scale give that it was an abstract.248 Both observational studies had a mean total quality score of 5, and a level of applicability of III.249, 302
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Carlson, 1987 US: 4 wk parallel RCT250 | MaxEPA preterm formula (n=30) | Preterm formula (n=31) | NS in Δ wt at 4 wks | n/a | Jadad total: 2 [Grade: C]; Schulz: Unclear | II |
| Carlson, 1992 US: up to 57wk PCA parallel RCT185 | marine oil (DHA+AA) formula (n=31*) | Control formula (n=34*) | S↓ wt, L, HC in marine oil at 40, 48, 57, 68, 79, 93 wks PCA+ | wt & L z-scores correlated + with plasma & RBC AA at 2,4,5,6,9, 12 mo | Jadad total: 4 [Grade: A]; Schulz: Adequate | II |
| HC correlated + plasma & RBC AA at 2, 4 mo | ||||||
| Uauy, 1992 US: 6 mo parallel RCT212 | Soy/ marine oil formula (n=22)/ HM (n=10) | Soy oil formula (n=18)/ corn oil formula (n=20) | NS in wt, L, HC, TST, SST at 3, 9, 17, 26 wks | S correlation (-) between RBC AA at 57 wk & length z score at 57 wks PCA | Jadad total: 2 [Grade: C]; Schulz: Unclear | II |
| Koletzko, 1994 Germany: 3 wk parallel RCT251 | Egg lipids + primrose oil formula (DHA+EPA) (n=9) | Control formula (n=10)/ HM (n=8) | NS in wt, L, HC at 3 wks | n/a | Jadad total: 2 [Grade: C]; Schulz: Unclear | III |
| Carlson, 1996, US: 5 mo parallel RCT191 | Marine oil (DHA +EPA) formula (n=26) | Control formula (n=33) | S↓ wt, L, HC in LCPUFA at 6+, 9++ mo PT | S (-) correlation between wt-for-L & RBC PE DHA at 5 mo | Jadad total: 3 [Grade: B]; Schulz: Unclear | II |
| S (+) correlation between L & RBC PC AA at 5 mo | ||||||
| Faldella, 1996 Italy: up to 52 wk PCA parallel RCT198 | DHA+EPA formula (n=23) | Control formula (n=26)/ HM (n=17) | NS in Δ wt, ΔL, ΔHC at 52 wks PCA | n/a | Jadad total: 1 [Grade: C]; Schulz: Unclear | III |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
= completed study;
PCA = postconceptional age;
ITT = intention to treat study;
HM = human milk group;
wt = weight;
L = length;
HC = head circumference;
Δ = change;
RBC = red blood cells;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower;
PE: phosphatidyl ethanolamine;
PC: phosphatidyl choline;
TST = triceps skinfold thickness;
SST = subscapular skinfold thickness
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Innis, 2002, US, Canada: 28 d multiceneter parallel RCT201 | DHA+AA formula (n=66) | DHA formula (n=66)/ control formula (n=62) | S↑ Δ wt in DHA+AA than in control at 40 wks PMA++ | S (+) correlation between Δ wt & RBC PE AA at 8 wks S | Jadad total: 3 [Grade: B]; Schulz: Unclear | I |
| S↑ wt, L, wt-to-L in DHA+AA than in DHA at 48 wks PMA++ | (+) correlation between wt, L & RBC PE AA at 8 wks | |||||
| S↑ wt, wt-to-L in DHA+AA than in control at 48 wk PMA++ | ||||||
| NS in HC at 48, 57 wk PMA | ||||||
| Groh-Wargo, 2002, Canada, US: 12 mo CA parallel RCT256 | LCP-1 (n=18) | LCP-2 (n=18)/ control formula (n=21) | NS in GP at 12 mo CA | n/a | Not assessed | X |
| Koletzko, 2003 Germany: 28 days parallel RCT257 | LCP formula (n=15) | Control formula (n=15)/ HM (n=19) | NS wt, L, HC at 28 d | n/a | Jadad total: 3 [Grade: B]; Schulz: Unclear | III |
| Fewtrell, 2004 UK: 9 mo CA parallel RCT258 | LCPUFA formula (n=122) | Control formula (n=116) | (ITT) S↑ Δ wt, ΔL in LCPUFA than in control at 9 mo CA+ | n/a | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
| NS in HC at 9 mo CA NS in PG at 18 mo CA | ||||||
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
ITT = intention to treat;
HM = human milk group;
wt = weight;
L = length;
HC = head circumference;
GP = growth parameters;
PMA = post menstrual age;
PT = post term;
CA = corrected age;
Δ = change;
RBC = red blood cells;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower
All of the included studies assessed the effect of omega-3 FA content of infant formula on growth patterns in preterm human infants. One study evaluated the effect of maternal breastfeeding together with the intake of omega-3 FA supplemented formula on growth patterns in preterm infants, as well as the effect of omega-3 FA content of infant formula on growth parameters.253 With the exception of the three Carlson et al. studies,185, 191, 250 as well as the studies of Clandinin et al.,193 Groh-Wargo et al.256 and Fewtrell et al.,258 all studies included a non-randomized group of breastfed infants that served as a reference standard.
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Vanderhoof, 1997, US: Up to 48 wk PCA parallel RCT218 | Microbial fermentation (DHA+AA) formula (n=77) | Control formula (n=78)/ HM (n=133) | S↑ wt, L, HC, MAC in LCP & control than in HM at 40 wk PCA+ | n/a | Jadad total: 4 [Grade: A]; Schulz: Adequate | I |
| NS in L, HC at 48 wks PCA S↑ L, MAC in LCP than in HM at 48 wks PCA | + | |||||
| NS in wt, L, HC at 92 wks PCA | ||||||
| Lapillonne, 1997, France: 4 mo CA parallel RCT252 | DHA+ EPA formula (n=11) | Control formula (n=12)/ HM (n=10) | NS in GP at 4 mo CA | n/a | Not assessed | X |
| Martinez, 1999, Brazil 30 d parallel RCT259 | Egg-lipid + primrose oil (formula (n=20) | Control formula (n=20)/ HM (n=18) | NS in wt, L, HC at 30 d | n/a | Jadad total: 1 [Grade: C]; Schulz: Unclear | III |
| Woltil, 1999, Netherlands 6 wks parallel RCT225 | High-DHA formula (n=16)/ HM (n=33) | Low-DHA formula (n=13) pb-1 (n=13)/ pb-2 (n=37)/ pb-3 (n=31) | NS in Δ wt, ΔL, & ΔHC between LCP-1, LCP-2 & pb at 1 mo | S (+) correlation between Δwt, ΔL, ΔHC & plasma & RBC DHA at 1mo | Jadad total: 1 [Grade: C]; Schulz: Unclear | III |
| S↑ Δ wt, ΔL, Δ brain wt, ΔHC in pb-1 than in pb-2 & pb-3 at 1mo+ | ||||||
| Ghebremeskel1999, UK: 11 wk parallel RCT253 | Egg-lipid+ primrose oil (DHA+AA) +HM (n=12)/ control formula (n=8) | LCP formula (n=7)/ control formula+HM/ (n=14)/ HM (n=20) | NS in wt, L, HC at ≈11 wk among 5 grps | n/a | Jadad total: 2 [Grade: C]; Schulz: Unclear | III |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
= mg/kg/day;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
PCA = post conceptional age;
CA = corrected age;
HM = human milk group;
wt = weight;
L = length;
HC = head circumference;
MAC = mid arm circumference;
Δ = change;
GP = growth parameters;
RBC = red blood cells;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Bougle, 1999, France: 1 mo parallel RCT254 | LCP formula (n=14) | Control formula (n=11)/ HM (n=15) | S↑ Δ wt in LCP than in HM at 1 mo+ | n/a | Jadad total: 3 [Grade: B]; Schulz: Unclear | III |
| NS in wt, L, HC, ΔL, & Δ HC at 1 mo+ | ||||||
| Field, 2000 Canada: 5.5 wk parallel RCT303 | LCP formula (n=15) | Control formula (n=12)/ HM (n=17) | S↓ Δ wt in HM than in LCP & pb at 28 d+ | n/a | Jadad total: 1 [Grade: C]; Schulz: Unclear | II |
| NS in L, HC at 35 d+ | ||||||
| O'Connor, 2001 US, UK, Chile: 12 mo CA parallel RCT207 | DHA+AA(Fish/ fungal oil) formula (n=140) | DHA+AA (Egg-TG/ fish oil) formula (n=143)/ control formula (n=144) | (ITT) NS Δ wt, ΔL, Δ HC at 8 wk, 4 mo, 12 mo CA | S (+) correlation rate wt gain & RBC PE AA at 28 d | Jadad total: 3 [Grade: B]; Schulz: Unclear | I |
| wt & L S correlated RBC PE AA at 28 d | ||||||
| Fewtrell, 2002 UK: 9 mo CA parallel RCT273 | LCPUFA formula (n=95) | Control formula (n=100)/ HM (n=88) | (ITT) S↓ wt, L in LCPUFA than in pb at 9, 18 mo CA+ | n/a | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
| NS in HC at 9, 18 mo CA | ||||||
| Clandinin 2002 Canada: 57 wk PMA parallel RCT193 | DHA+AA (SCO) (n=112) | DHA+AA (fish oil) (n=130)/ control formula (n=119) | NS in GP at 40, 57 wks PMA | n/a | Not assessed | X |
| S↑ wt in DHA+AA (SCO) than in control at 66–118 wks PMA+ | ||||||
| S↑ L in DHA+AA (SCO) than in other 2 formulas at 79, 92 wks PMA+ | ||||||
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
HM = human milk group;
wt = weight;
L = length;
HC = head circumference;
AC = arm circumference;
Δ = change;
RBC = red blood cells;
PE = phosphatidyl ethanolamine;
PC = phosphatidylcholine;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower;
PMA = postmenstrual age;
GP = growth patterns;
CA = corrected age;
SCO = single cell oil;
TG = tryglicerids
Study characteristics. All studies were parallel RCTs with at least two groups, although the study of Ghebren et al. involved five feeding groups.253
The inclusion/exclusion criteria were described by 11 of 20 studies.198, 201, 207, 212, 218, 250, 251, 253, 257, 259, 303 Only inclusion criteria were reported in four studies225, 254, 258, 273 and only exclusion criteria were reported in two studies.185, 191 Three studies failed to report either inclusion or exclusion criteria.193, 252, 256 Three studies defined maternal substance abuse (cocaine and alcohol) history as exclusion criteria.191, 207, 218 The definition of a preterm infant (<37 weeks GA) was described in eight studies,198, 251, 253, 254, 258, 259, 273, 303 although included preterm infants in these studies were at different GAs. Koletzko et al.251 and Fewtrell et al.273 included infants less than 37 weeks GA, whereas, Field et al.303 evaluated infants born at less than 36 weeks GA, Fewtrell et al.258 at less than 35 weeks GA, Bougle et al.254 at less than 34 weeks GA, and Faldella et al.198 and Ghebremeskel et al.253 at less than 33 weeks GA. Eight studies were typically small, with a mean of 30 participants (range 19–41).251–254, 256, 257, 259, 303 The study duration ranged from 3 weeks to 12 months.
The trials were conducted in various countries, with five undertaken in the U.S.,183, 185, 191, 212, 218, 250 three in the U.K.253, 258, 273 and Canada,193, 201, 303 two in France252, 254 and Germany,251, 257 one in Italy,198 one in Brazil,259 and one in The Netherlands.225 One multicenter study was conducted in three countries—the U.S., U.K and Chile.207 Groh-Wargo et al. failed to indicate the country where their study was undertaken.256
The study of Carlson et al.250 was supported by Ross laboratories, Columbus, OH. Another Carlson et al. study was sponsored by Ross Laboratories, Columbus, OH, and the National Eye Institute.185 Koletzko et al. received a grant from Deutsche Forschungsgemeinschaft, Bonn, Germany and Milupa AG, Friedrichsdorf, Germany.251 Uauy et al.'s study was financially supported by the National Institute of Health.212 The Carlson et al. study191 was funded by the National Eye Institute, the National Institute of Child Health and Human Development, and Ross Products Division, Abbott Laboratories, Columbus, OH. Vanderhoof et al.'s study was supported by Wyeth Nutritionals International, Philadelphia, Pennsylvania, U.S.A.218 Martinez et al. was funded by the Brazilian Research Council and Milupa GmbH.259 Woltil et al.'s study was supported by grants from Friesland Nutrition, Leeuwarden, The Netherlands.225 The study of Ghebremeskel et al. was financed by The Christopher H.R. Reeves Charitable Trust and Milupa Plc.253 Field et al.'s study was supported by grants from the Natural Sciences and Engineering Research Council of Canada and the Medical Research Council of Canada, as well as Wyeth-Ayerst Research.303 Fewtrell et al.'s study was funded by Numico Research BV (Wageningen, The Netherlands).273 Clandinin et al.'s193 and Innis et al.'s201 studies were financed by grants from Mead Johnson & Company. The Groh-Wargo et al. study was supported by Abott Laboratoris, Columbus and GCRC NIH.256 Koletzko et al.'s study was sponsored by Deutsche Forschungsgemeinschaft, Bonn, Germany, Nestec S.A., Vevey, Switzerland and Nestle Alete GmbH, Munchen, Germany.257 Fewtrell et al.'s study was supported by grant from H.J. Heinz Company, Ltd, Hayes, Middlesex, U.K.258 Four trials did not provide information concerning their funding source.198, 207, 252, 254
In general, six studies193, 201, 218, 225, 250, 258 were granted only by pharmaceutical companies, six studies185, 191, 251, 256, 257, 303 by both pharmaceutical and governmental fundings, two studies212, 273 by only governmental sources, and one study253 partly by private and pharmaceutical sources.
Pre-study sample size calculation to reach statistical significance and power was performed in seven studies.191, 201, 207, 212, 218, 258, 273
Population characteristics. A total of 2,650 preterm infants were enrolled across 20 RCTs. The total number of infants that completed the trials could not be calculated since six of the studies failed to report these data, providing only the number of infants who entered the trial.193, 218, 225, 252, 256, 259
Eligibility criteria varied broadly across studies. Most importantly, body mass of recruited preterm infants, GA, and age at study enrollment, differed substantially from trial to trial. Some investigators randomized very small preterm infants (i.e., weighing less than 1,400 g to 1,500 g),185, 201, 212, 250, 259 whereas, other authors broadened their criteria to include preterm infants with a birth weight ranging from 2,000 g to 2,500 g.218, 225, 258 Six studies failed to report predefined eligibility criteria regarding infant's weight.191, 198, 253, 254, 256, 303
The gender distribution of randomized infants was reported in ten studies.191, 207, 212, 218, 225, 257–259, 273, 304 In eight of these studies, male infants constituted the majority of participants, although the gender ratio of infants among different diet groups were evenly distributed in all of these studies.
The racial/ethnic background of study participants were described in only four trials.191, 207, 212, 218 In two studies,191, 212 the majority of infants were Black, accounting for 60% and 83% of study population, respectively. In the two other trials,207, 218 White infants comprised the majority of study participants accounting for 58% and 70% of participants, respectively.
Different variables were used to demonstrate family sociodemographic status in the studies (e.g., maternal education, social class, professional qualification, home inventory score, maternal WAIS-R raw vocabulary score). Maternal social status was determined in two studies,258, 273 whereas, information about maternal education or maternal professional qualification was given in three trials.207, 258, 273 O'Connor et al. measured and compared the quality and quantity of stimulation and support available to a child in the home environment in different groups by means of a HOME inventory score. Maternal intelligence was assessed by administering a WAIS-R raw vocabulary score.207 There were no differences in sociodemographic variables among the study groups of randomized infants in all of these studies with the exception of HOME inventory scores, which were better in the control group than in both treatment groups.207 Mothers of infants in the reference breastfed group had a more prestigious social score and attained a higher level of professional qualification compared with mothers of formula-fed infants.273
Only one study reported on maternal smoking during pregnancy and postnatal smoking in the home.207
Intervention/exposure characteristics. Only one of 20 reviewed studies reported the exact amount of supplementary LCPUFAs consumed per day by the preterm infants.225 Woltil et al.225 assigned preterm infants to two LCPUFA-supplemented feeding groups with different anounts of DHA—group LCP-1 consumed 23.3±9.9 mg/kg/day DHA, whereas group LCP-2 consumed 13.3 to 41.8 mg/kg/day DHA. The rest of the studies failed to indicate daily consumption of omega-3 FAs by feeding infants. In all studies, formula-fed infants received preterm formula and depending on the ultimate interest of the research project, went to either post-discharge or term formula. In fourteen studies, the effect of only preterm formulas with supplemented LCPUFAs on growth indices of preterm infants were assessed.191, 193, 198, 212, 218, 225, 250, 251, 253, 254, 257, 259, 273, 303 In six studies, infants continued to receive a formula designed for term infants (with or without LCP supplementation) according to their original assignments, and their effect on each child's growth was further estimated.185, 201, 207, 252, 256, 258
Preterm infants were eligible to enter the study after they attained full enteral feeding without intravenous support. The minimum amount of formula-intake required in order to be considered fully enteral-fed differed across the trials. In two studies infants became eligible to enroll when they received at least 130 mL/kg/day of a preterm formula.251, 257 Carlson et al. allowed preterm infants to enroll in the study after they had reached intakes of nutrient-enriched formula of at least 60 kcal/kg/day,250 whereas, Carlson et al. established criteria for enrollment of more than 110 kcal/kg/day.185 Enteral feeding of at least 70 to 120 kcal/kg/day was required in the trial of Uauy et al.;212 Carlson et al. required an intake of at least 100 kcal/kg/day.191 Vanderhoof et al. specified an intake of 145 mL/kg/day,218 whereas, Woltil et al. required an intake of 80 kcal/kg/day.225 In the Martinez et al. study, an intake of 112 kcal/kg/day was indicated259 and Innis et al. specified an intake of at least 90 kcal/kg/day.201 Eight studies failed to report a minimum daily food or caloric intake required for preterm infants.198, 207, 253, 254, 256, 258, 273, 303
Only two studies reported as part of the protocol that the volume of formula consumed, i.e., calculated as the difference in the volume of formula in the bottle at the start and end of the feed, was recorded.185, 225 Daily intake of formula did not differ in the three feeding groups of Woltil et al. (171 [SD=21] mL/kg vs 172 [SD=17] mL/kg vs 176 [SD=17] mL/kg).225 In a study of Carlson et al.,185 all except one infant consumed at least 720 g of formula per day through 79 weeks PCA. Duration of formula feeding ranged from 3 weeks251 to 12 months CA.207, 256
The sources of omega-3 FA intervention varied across the RCTs. Three trials described the source of LCPUFA supplementation as purely fish oil.225, 250, 252 The specific type of fish from which fish oil exposures were derived was described in only one study.258 O'Connor et al.207 and Groh-Wargo et al.256 used a treatment formula with omega-3 FAs derived from fish and fungal oils, whereas, Fewtrell et al.258 supplemented a treatment formula with a combination of DHA derived from fish oil and AA derived from borage oil. The remaining studies employed either single cell sources of FAs,193, 201, 218, 303 marine oils,185, 191, 212 egg phospholipids with primrose oil,253, 259, 273 or a combination of egg triglyceride and fish oil sources.207, 256, 257 The sources of supplemental LC PUFAs were not reported in three trials.198, 251, 254
The type of omega-3 FA employed in four studies included a combination of DHA and EPA;185, 191, 225, 252 DHA alone was used in one trial.201 Supplementation of formulas with omega-6 FA AA was reported in 12 studies.193, 198, 201, 207, 213, 218, 253, 254, 256, 258, 273, 303
Seven studies failed to report the name of feeding formulas, although all of them indicated the manufacturers of the product.185, 193, 212, 225, 252, 254, 256 The brands of formulas employed in the rest of the studies were: Enfamil Premature (Mead Johnson Nutritionals, Evansville, Ind);201, 250 Similac Special Care (Ross Laboratories, Columbus, OH);191, 207, 250 Prematil with Mipupan (Milupa, AG, Friedrichsdorf, Germany);198, 251, 253, 259, 273 SMA “Preemie” (Wyeth-Ayerst Laboratories, Randor, Philadelphia, PA);218, 250, 303 Alprem (Nestle, Vevey, Switzerland);257 OsterPrem with LCPUFA (Heinz Co, Ltd, Hayes, Middlesex, U.K.);258 NeoSure (Ross Product Division, Columbus, OH, USA);207 and, Farley's PreCare with LCPUFA (Heinz Co, Ltd, Hayes, Middlesex, U.K.) were used as a term formulas after hospital discharge. Five studies indicated the manufacturer of at least one omega-3 FA product used in their study.201, 212, 218, 250, 303 In three of these trials supplemented LCPUFAs were manufactured and supplied by Market Biosciences Corporation (Columbia, MD, USA),201, 218, 303 whereas, in two other studies omega-3 FAs were produced by MaxEPA, R.P. Scherer, Troy, MI250 and Zapata-Haynie Co., Reedville, Va.212 Only one study reported on the purity of their omega-3 FA exposure.225
Formula was the only source of alimentation in 14 studies and no solid foods were introduced during the entire trial period.185, 191, 193, 198, 201, 218, 225, 250, 251, 253, 254, 257, 259, 303 Only one study reported the time of introduction of solid foods—Uauy et al.212 permitted cereals, fruit juices, or fruits at 4 months of CA in both study groups. Fewtrell et al.,273 Groh-Wargo et al.,256 Fewtrell et al.,258 and O'Connor et al.207 did not report of any solid food introduction to infants even though their study durations were up to 9 and 12 months CA.
Information about caloric balance of feeding formulas was reported in eight RCTs.185, 191, 201, 212, 225, 254, 259, 273 Nutritional and energy intake were similar between randomized groups throughout the study period in the majority of trials. However, Carlson et al. reported that the mean energy intake from formula was not affected by dietary assignment or gender at 48 and 57 weeks PCA; however, at 68 weeks PCA, infants consuming the marine oil-supplemented formula had significantly higher energy intake from formula compared with infants fed standard formula.185
Only three RCTs212, 258, 273 mentioned that study treatment formulas were indistinguishable in appearance and odor. Uauy et al. also reported that supplemental marine oil was winterized and stabilized.212
Cointervention characteristics. Six studies reported the content of vitamin and mineral supplements of feeding formulas or multivitamin preparations taken by preterm infants.191, 207, 212, 251, 253, 303 All of these formulas or oral vitamin supplements provided alpha-tocopherol ranging from 4.5 mg/day303 to 15 mg/day.253 Ghebremeskel et al. used a formula also supplemented with 0.22 μmol/100 mL vitamin A.253 The formula used by O'Connor et al.207 was supplemented with 0.60 mg/L vitamin A and 0.50 mg/L beta-carotene, and Field et al. added 1200 U/day vitamin D to their infant formulas.303
Due to the physical immaturity of LBW preterm infants, many of the newborns required pre- or on-study medical cointerventions, such as oxygen supply, mechanical ventilation, intravenous nutrition, blood or blood product transfusion, and corticosteroid treatment. The most frequently reported cointervention was oxygen supply or mechanical ventilation and measurements were provided in four studies.185, 191, 212, 258 Carlson et al.191 allowed a significant subgroup of patients (n=23) who continued to require supplemental oxygen for 28 days and had lung changes on X-ray characteristic of bronchopulmonary dysplasia, to remain in the study. Two studies reported use of blood or blood products.212, 303 Uauy et al. described that only five preterm infants required blood transfusion after random assignment, and all transfusions were given at least 2 weeks before blood sampling.212
In the study of Field et al., two infants received an intravenous bolus of albumin on day 2 of life.303 Some investigators set strict inclusion criteria for infants requiring additional medical treatment. Vanderhoof et al., for example, excluded preterm infants with consistent requirements for oxygen at 36 weeks PCA and administration of more than a 5-day course of corticosteroids.218 In studies of Koletzko et al.251 and Koletzko et al.,257 infants requiring artificial ventilation or an oxygen supply with FiO2 >0.3 at the time of enrollment were excluded. Uauy et al. reported that no infants had used a ventilator after day 5 or for more than 3 days.212 None of the participants received corticosteroids, red blood cells and plasma transfusions or intravenous lipid emulsions beyond day 8 of life in the Field et al. trial.303 However, none of these studies reported how many newborn babies received cointerventional measures below the set limit.
Outcome characteristics. Of 20 trials, 12 assessed the growth parameters as primary outcomes123, 150, 305–314 while the remaining eight trials evaluated them as a secondary outcome or part of the safety profile. Thirteen included RCTs employed infants' weight, length, and HC as main outcome measures for growth.185, 191, 193, 201, 212, 218, 251, 253, 254, 257, 259, 273, 303 Two trials (abstracts) did not specify the growth indices evaluated, rather they described changes in growth parameters.252, 256 Carlson et al. evaluated only weight gain from birth to 4 weeks of study period in two randomized dietary groups.250 The rate of gain in weight, length and HC were assessed in five studies.198, 207, 225, 254, 258 Triceps skinfold thickness and subscapular skinfold thickness were measured in two RCTs.212, 259 Another study evaluated mid-arm circumference,218 another measured weight-to-length ratio,201 and one study used estimated brain weight gain in preterm infants as one of the growth outcomes.225
| Study Quality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| A | B | C | ||||||||
| Applicability | I | Author | Year | n | Author | Year | n | Author | Year | n |
| VanderhoofA | 1997 | 288 | O'ConnorU | 2001 | 470 | |||||
| InnisU | 2002 | 194 | ||||||||
| II | Author | Year | n | Author | Year | n | Author | Year | n | |
| CarlsonA | 1992 | 79 | CarlsonU | 1996 | 36 | CarlsonU | 1987 | 61 | ||
| FewtrellA | 2002 | 283 | UauyU | 1992 | 81 | |||||
| FewtrellA | 2004 | 238 | GhbremeskelU | 1999 | 61 | |||||
| FieldU | 2000 | 44 | ||||||||
| III | Author | Year | n | Author | Year | n | Author | Year | n | |
| KoletzkoU | 2003 | 49 | KoletzkoU | 1994 | 27 | |||||
| BougleU | 1999 | 40 | FaldellaU | 1996 | 66 | |||||
| WoltilU | 1999 | 143 | ||||||||
| MartinezU | 1999 | 40 | ||||||||
n = number of allocated/selected participants;
RCT = Adequate vs UUnclear allocation concealment
The most frequently investigated outcomes across the reviewed studies were infant weight, length, and HC. Weight and/or weight gain was evaluated in all trials, and infant's length and/or length gain was evaluated in all but one250 trial. The majority of the studies did not find any statistically significant difference between randomized groups regarding these two parameters at different time points. Carlson et al.,250 who randomized preterm infants to receive either preterm control formula or MaxEPA supplemented infant preterm formula for 4 weeks, did not find any better weight and length gain in the treatment group. Similar results were obtained at 3 weeks in the study of Koletzko et al.,251 at 3, 9, 17, and 26 weeks in the study of Uauy et al.,212 at 52 weeks PCA in the Faldella et al. study,198 at 92 weeks PCA in the Vanderhoof et al. study,218 at 4 months of CA according to Lapillonne et al.,252 a mean of 11 weeks according to Ghebremeskel et al.,253 at 1 month in three studies.,225, 254, 259, at 8 weeks, 4, and 12 months CA in the study of O'Connor et al.,207 at 40 and 57 weeks postmenstrual ages in Clandinin et al.,193 at 12 months CA according to Groh-Wargo et al.,256 and at 28 days of age in the study by Koletzko et al.257
Three studies revealed statistically significant weight and length gain in LCPUFA-supplemented diet groups compared with placebo.193, 201, 258
Clandinin et al. randomized LBW infants to one of three feeding groups: (1) control LCP-1 (DHA [17mg/100kcal] and AA [34mg/100kcal] derived from single cell oils); (2) LCP-2 (DHA [17mg/100kcal] derived from fish oil); or, (3) AA (34mg/100kcal, derived from single cell oils).193 The study found a significantly higher weight in the LCP-1 group of infants compared with infants in in the placebo group at 66 weeks to 118 weeks postmenstrual ages. In addition, infants in the LCP-1 group were significantly longer than infants in the LCP-2 or placebo groups at 79 to 92 weeks postmenstrual ages.193
Innis et al., who randomly assigned VLBW (846g-1560g) infants to receive either preterm control formula (no DHA or AA), preterm formula containing only DHA (0.15wt%; DHA group) or DHA+AA formula (DHA [0.14wt%] and AA [0.27wt%]; DHA+AA group), found significantly higher body weight, length and weight-to-length ratio in infants in the DHA+AA group compared with those in the DHA formula group, and significantly higher body weight and weight-to-length ratio in DHA+AA group compared with those in the control group at 48 weeks postmenstrual age.201 Moreover, infants fed the DHA+AA formula gained weight significantly faster during premature formula feeding than infants fed the control formula. The rate of weight gain of infants fed the formula with DHA was not different from that of infants fed the control formula or the formula with DHA+AA.201
The study of Fewtrell et al. involving preterm infants with a birth weight less than 2,000 g and GA less than 35 weeks, found a significantly greater increase in weight and length of infants in the LCPUFA-supplemented formula group (DHA [0.5wt%], EPA [0.1wt%], and AA [0.04wt%]) compared with infants fed unsupplemented control formula at 9 months CA.258
Contrary to these findings, three trials revealed statistically significant weight and length gain in infants in the placebo group compared with the LCPUFA-supplemented group, suggesting that omega-3 LCPUFA can have a negative effect on growth of very-low-birth infants.185, 191, 273
The trial of Carlson et al.185 that compared growth parameters in preterm, premature infants weighed less than 1400 g fed marine oil-enriched preterm infant formula with infants in a placebo group, found that by 40 weeks and continuing throughout infancy (i.e., up to 93 weeks PCA), infants supplemented with marine oil had significantly lower normalized weight, length, HC and weight-to-length ratio than those receiving standard formula.185
Carlson et al. randomly assigned preterm infants with or without bronchopulmonary dysplasia to receive standard preterm formula, or a formula that provided n-3 LCPUFAs from marine oil (DHA [0.2wt%] and EPA [0.06wt%]).191 The investigators reported that n-3 LCPUFA-supplemented infants weighed significantly less than placebo group babies both at 6 and 9 months post term and had significantly lower weight-to-length ratios at 2, 6, 9, and 12 months post term.191
Fewtrell et al observed that at 9 and 18 months CA, treatment formula infants were significantly lighter and shorter than control group babies. This weight difference was present in both boys and girls, and it remained significant at 18 months after adjusting for parental smoking, social class, and level of maternal education. 273
In the three studies where a weight and length gain benefit was observed in LCPUFA supplemented formula fed infants,193, 201, 258 investigators used experimental formulas containing AA. Conversely, in trials that showed a decrease in weight,185, 191, 273 length,185, 191, 273 and HC185, 191 in infants fed LCPUFA-supplemented formula, the formula did not contain AA. It can be assumed that the growth benefit in preterm infants might be attributed to supplemented AA, and omega-3 FAs negatively affect infant weight gain.
Infant HC and/or HC gain was evaluated in all but two trials.193, 250 Most of the studies did not find any statistically significant difference between randomized groups regarding this parameter at different time point. Only two studies185, 191 reported a significantly lower HC in the omega-3 FA supplemented group compared with the placebo group at 40 to 93 weeks PCA185 and at 6 and 9 months post term.191 None of the studies revealed any benefit of LCPUFA supplementation regarding the HC gain of premature infants.
Other growth outcomes assessed were triceps skinfold thickness, subscapular skinfold thickness, and mid-arm circumference. Uauy et al. did not find any statistically significant difference in triceps skinfold thickness and subscapular skinfold thickness among the randomized study groups at 3, 9, 17, and 26 weeks.212 Martinez et al. had the same result at 30 days.259 Vanderhoof et al. did not find a statistically significant difference in mid-arm circumference between study groups, although this parameter was significantly lower in the breastfed group.218
Carlson et al. found that the weight and length z-scores were positively correlated with the plasma and RBC AA content at 2, 4, 5, 6, 9, and 12 months of age. However, HC was positively correlated at 2 and 4 months of age only.185 Uauy et al. found that the length z-score at 57 weeks of PCA was negatively correlated with the RBC AA at 57 weeks PCA.212
The other Carlson et al. study reported a negative correlation between the weight-for-length z-score and the RBC PE DHA at 5 months of age, whereas, there was a positive correlation between length and RBC PC AA at 5 months.191 Innis et al. observed a positive correlation between the rate of weight gain and the RBC PE AA at 28 days (end of feeding), as well as the weight and length.201 Woltil et al. found a significantly positive correlation between the weight, length and HC gain and the plasma and RBC DHA content at 1 month of age.225
Finally, O'Connor et al. found a significantly postive correlation between the rate of weight gain, weight (mean) and length (mean) and the RBC AA at 1 month of age.207
The outcomes considered for meta-analysis for growth development were weight, height and HC at 4 and 12 months. These end-points were selected given that the intervention with supplemented formula was exclusively administered until 4 months and 12 months (as a longterm followup measure), yet with the possible confounder factor of the background diet. Outcome results were available for more than one study at six different end-points in time: CA 4, 6, 9, 11, 12, and 18 months in 19 studies.
At 4 months CA, outcomes were available for four studies.185, 191, 201, 207 Carlson et al.185 provided growth z-scores with standard deviation in a figure, and reported absolute growth data (by sex) in a table but without any measure of variability. In another report by Carlson et al.191 supplementation only continued to 2 months CA. Innis et al.201 did not report HC data on the grounds that results were not found to be statistically significant. We were thus able to combine weight and length results from Innis et al. and O'Connor et al.201, 207 Both trials assessed these outcomes as primary outcomes.
At 12 months CA, outcomes were available for three studies.185, 191, 207 Supplementation in Carlson et al.191 only continued until 2 months CA.
Supplementation in Carlson et al.185 continued only until 9 months CA. In addition, Carlson et al.185 provided growth z-scores with SD in a figure, and absolute growth data (by sex and without any measure of variability) in a table. We were thus unable to combine any results.
Meta-analysis was performed using the random effects weighted mean difference.
The mean weight difference (WMD) in weight (kg) and length (cm) at 4 months (DHA+AA vs. control) in two studies201, 207 were nonstatistically significant. For weight: WMD: 0.04, CI 95%: -0.30; 0.38. For length: WMD: 0.09, CI 95%: -0.62; 0.80.
In the majority of the RCTs there was no evidence that randomization failed to produce comparable groups with the exception of scores on the HOME Inventory.268 In the study of O'Connor et al.,268 HOME Inventory scores were higher (better) in infants weighing less than 1,250 g randomized to the control group than those randomized to the fish/fungal oil group. HOME Inventory scores were lower in infants in the more than 1,250 g birth weight stratum randomized to the egg-TG/fish oil group compared with scores in the control and fish/fungal oil groups.268
Carlson et al. used a multiple regression analysis to control for potential effect modifiers such as maternal height, marine oil supplementation, and birth order.185 Length achieved at 12 months of age was positively associated with maternal height, but negatively associated with marine oil supplementation. Weight was negatively associated with both birth and marine oil supplementation.185
Fewtrell et al. controlled the growth changes for covariates like gender, center, parental smoking, social class and level of maternal education.273
Differences in weight and length at 18 months post-term remained after adjusting for parental smoking, social class and level of maternal education.273 There were no differences in HC between groups. The growth differences were greater in one center than the other, however, there was no interaction between center and growth patterns.273 O'Connor et al. observed that the females in the DHA+AA (egg-TG/fish) group had a greater mean HC gain from day 1 to term CA compared with the females in the other groups.207
The power calculation was reported in eight trials,123, 307, 310, 312, 315, 316, 321, 322 while the intention-to-treat analysis approach was reported in only three studies.310, 321, 322
Eighteen double-blinded RCTs met eligibility criteria for addressing the question relating to the possible effectiveness of formula intake enriched with omega-3 FA on growth patterns in term infants.104, 182, 203, 205, 223, 227, 260–270
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Ponder, 1992, US: 8 wk parallel RCT260 | Soy oil formula (n=11*) | Corn oil formula (n=14*)/ HM (n=18*) | NS in wt, L, HC at 3d, 4wk, 8wk | n/a | Jadad total: 1 [Grade: C]; Schulz: Unclear | II |
| Decsi, 1995, Hungary: parallel RCT261 | DHA+EPA+AA formula (n=10) | Control formula (n=12) | NS in Δ wt, ΔL, ΔHC at 4 mo | n/a | Jadad total: 1 [Grade: C]; Schulz: Unclear | III |
| Makrides, 1995, Australia: 30 wk parallel RCT262 | DHA+EPA+AA fish oil formula (n=13*) | Control formula (n=19*)/ HM (n=47*) | NS in wt, L, HC at 6, 16, 30 wks | NS correlation of RBC LCPUFA & GP | Jadad total: 2 [Grade: C]; Schulz: Unclear | II |
| Jensen, 1997, US: 120 d parallel RCT203 | F1 (LA/ALA 44) (n=20)/ F4 (LA/ALA 4.8) (n=20) | F2 (LA/ALA 18.2) (n=20)/ F3 (LA/ALA 9.7) (n=20) | S↓ wt in F4 than in F1 at 4 mo+ NS in L, HC, TST, & SST at 4 & 8 mo | S (+) correlation between W at 4 mo & plasma AA at 120d NS correlations between wt & plasma n-3 at 4 mo | Jadad total: 2 [Grade: C]; Schulz: Unclear | II |
| Innis, 1997, US, Canada: 3 mo MLT parallel RCT263 | LA/ALA 9.5 (n=69) | LA/ALA 7.3 (n=70)/ HM (n=99) | NS in wt, L, & HC at 3 mo | NS correlations between GP & plasma & RBC AA | Jadad total: 2 [Grade: C]; Schulz: Unclear | I |
| Auestad, 1997, US: 12 mo parallel104 | DHA+AA (n=46*)/ HM (n=63*) | DHA (n=43*)/ control formula (n=45*) | NS in wt, L, HC at 12 mo | n/a | Jadad total: 3 [Grade: B]; Schulz: Unclear | I |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
= number of participants who completed study;
HM = human milk group;
BW = birth weight;
BL = birth length;
wt= weight;
L = length;
HC = head circumference;
Δ = change;
RBC = red blood cells;
GP = growth parameters;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p <.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower;
HM = human milk;
GP = growth parameters;
TST = triceps skinfold thickness;
SST = subscapular skinfold thickness
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Lapillonne, 2000, France: 4 mo parallel RCT267 | DHA(fish oil)- low EPA formula (n=12) | Control formula (n=12)/ HM (n=13) | S↑ HC in control than in LCPUFA & HM at 4mo+ NS in wt, L, at 2, 4 mo | Jadad total: 1 [Grade: C]; Schulz: Unclear | III |
| Morris, 2000, UK: 12 wk parallel RCT268 | DHA-TGL formula (n=54*) | Control formula (n=55*) | S↑ SST in DHA at 6 wk & 3 mo+ NS at 6 mo & 12 mo NS in wt, L, HC, MAC, TST at 6 wk, 12 wk, 6 mo, 12 mo | Jadad total: 3 [Grade: B]; Schulz: Unclear | II |
| Auestad, 2001a, US: 12 mo parallel RCT227 | DHA+ AA (egg-TG) formula (n=80) | DHA+ AA (fish/fungal) formula (n=82)/ control formula (n=77) | NS in wt, L, HC at 1, 2, 4, 6, 9, & 12 mo S↑ wt gain in males in DHA+AA (egg) at 4 mo | Jadad total: 5 [Grade: A]; Schulz: Adequate | I |
| Auestad, 2001b, US: 1 y, parallel RCT227 | DHA + AA formula + HM (n=83) | Control formula + HM (n=82) | NS in wt, L, HC at 1, 2, 4, 6, 9, & 12 mo or in wt, L, HC gain | Jadad total: 5 [Grade: A]; Schulz: Adequate | I |
| Birch, 2002, US: 46 wk parallel RCT269 | LCP formula (n=32) | Control formula (n=33) | NS in wt, L, HC, TST & SST at 0,6,17,26 & 52 wks | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
| Hoffman, 2003 US: 7 mo Parallel RCT270 | DHA+AA formula (n=30) | Control formula (n=31) | NS in wt, L, HC, wt-for-L at 4,6,9 & 12 mo | Jadad total: 3 [Grade:B]; Schulz: Adequate | II |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
= number of participants who completed study;
HM = human milk group;
W = weight;
L = length;
HC = head circumference;
MAC = mid-arm circumference;
SST = sum of skinfold thickness;
TST = triceps skinfold thickness;
SST = subscapular skinfold thickness;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower
Jensen et al. randomly assigned 80 healthy term infants to receive one of four formulas as his/her sole source of nutrition from birth to 120 days of age.203 LA comprised 15.6% to 17.6% of the total FAs of all formulas. The ALA content was 0.4%, 1%, 1.7%, and 3.2% of total FAs, and LA/ALA ratios were 44, 18.2, 9.7, and 4.8, respectively.
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Jorgensen 1997, Denmark: 3 mo parallel RCT264 | DHA+GLA formula (n=12)/ HM (n=17) | DHA formula (n=14)/ Control formula (n=11) | NS in wt, L, HC, GV at 1, 2, & 4 mo | n/a | Jadad total: 2 [Grade: C]; Schulz: unclear | III |
| Birch, 1998, US: 17 wk parallel RCT182 | DHA+AA (n=26)/ HM (n=29) | DHA (n=26)/ control formula (n=26) | NS in wt, L, HC, TST, SST at 17wk | n/a | Jadad total: 5 [Grade: A]; Schulz: Adequate | I |
| Willatts, 1998, UK: 4 mo parallel RCT223 | DHA + AA formula (n=20) | Control formula (n=20) | NS wt, L, HC at 3 mo | n/a | Jadad total: 3 [Grade: B]; Schulz: Unclear | II |
| Makrides, 1999, Australia: 12 mo parallel RCT205 | DHA+AA formula (n=28)/ HM (n=63) | DHA formula (n=27)/ control formula (n=28) | NS in wt, L, HC at 6, 16, 34 wk, 12 mo & 24 mo | S (-) correlation of plasma DHA at 16 wks & wt at 12 mo & 24 mo | Jadad total: 5 [Grade: A]; Schulz: Adequate | III |
| Lucas, 1999, UK: 6 mo parallel RCT265 | LCPUFA formula (n=154) | control formula (n=155)/ HM (n=138) | NS in wt, L, HC, MAC, SST at 6, 9, 18 mo (ITT) | n/a | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
| Makrides, 2000, Australia: 34 wk parallel RCT266 | LA/ALA 10 formula (n=36) | LA/ALA 5 formula (n=37)/ HM (n=103) | NS in Δ wt, ΔL, Δ HC between 10:1-F & 5:1-F at 6, 16, 34 wks | n/a | Jadad total: 5 [Grade: A];Schulz: Adequate | II |
| S↑ wt at 6 wks & L at 16 wks in 5:1 F+ | ||||||
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
FAs = fatty acids;
HM = human milk group;
wt = weight;
L = length;
HC = head circumference;
RBC = red blood cells;
GV = growth velocity;
PC = phosphatidylcholine;
PE = phosphatidylethanolamine;
TST = triceps skinfold thickness;
SST = subscapular skinfold thicknessITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower
Study characteristics. All studies were parallel RCTs with at least two groups. All the studies evaluated the effect of omega-3 FA supplementations on infant growth. Auestad et al. also evaluated the effect of maternal breastfeeding together with omega-3 FA supplemented formula intake in term infants on growth pattern.227 Eleven of 18 studies also included a non-randomized group of breastfed infants that served as a reference standard.104, 182, 205, 227, 260, 262–267
The trials were conducted in various countries, with eight undertaken in the U.S.,104, 182, 203, 227, 260, 269, 270 three in Australia,205, 262, 266 three in the U.K.223, 265, 268 and one each in Denmark,264, France,267 and Hungary.261 The only multicenter study was conducted in the U.S. and Canada by Innis et al.263 Ponder et al.'s study was supported by Ross Laboratories, Columbus, OH.260 Decsi et al.'s study was sponsored by Deutsche Forschungsgemeinschaft, Bonn, Germany and Milupa Austria, Puch, Austria.261 Makrides et al. received grants from Channel 7 Children's Medical Research Foundation, Nestle Australia, Scotia Pharmaceuticals, U.K. and the Flinders Medical Center Research Foundation.262 Jensen et al.'s study was financially supported by the U.S. Department of Agriculture, Agricultural Research Service, Mead-Johnson Nutritional Group, The Foundation Fighting Blindness, Research to Prevent Blindness, Inc. and Retina Research Foundation.203 The Innis et al. study was funded by Mead Johnson Research Center, Evansville, IN.263 Auestad et al.'s study was supported by Ross Products Division, Abbott Laboratories.104 Makrides et al.'s was supported by Wyeth Nutritionals International, USA the Australian National Health and Medical Research Council, and the MS McLeod Research Trust.266 The study by Birch et al. was financed by the National Institutes of Health and Mead Johnson Nutritionals Research, Evansville, IN.182 The second Makrides et al. study was funded by Nestec Ltd, Swirzerland and the Australian National Health and Medical Research Council.205 Jorgensen et al.'s study was supported by grants from the Food Technology Research and Development Program (FOTEK), BASF Health and Nutrition, Denmark, and the Swedish Medical Research Council.264 Lucas et al.'s was funded by Nestec Ltd (Switzerland).265 Both of Auestad et al.'s trials were supported by Ross Products Division, Abott Laboratoris, Columbus, OH.227 The Lappilonne et al. study was supported by Bledina sa., Villefranche, France.267 Birch et al. and Hoffman et al. were supported by the NIH.269, 270 Only one trial conducted in U.K. did not provide information concerning its funding source.268 Willatts et al. was supported by Milupa Ltd.223
In general, eight studies were funded by grants only from pharmaceutical companies,223, 227, 260, 263, 265, 265, 267 seven studies were funded by both pharmaceutical and governmental agencies,104, 182, 203, 205, 261, 262, 264 two trials were funded by governmental sources alone,269, 270 and one study was funded partly by private, pharmaceutical and governmental sources.266
The pre-study sample size calculation to reach statistical significance and power was done in nine studies.182, 205, 223, 227, 262, 265, 269, 270
Population characteristics. The total number of enrolled children across the 18 RCTs was not possible to calculate because two investigators104, 260 failed to report this data providing only the number of infants who finished the study. The sample sizes ranged from 22261 to 447.265
The percentage of male randomized infants was reported in five studies205, 264, 265, 269, 323 and ranged from 42% to 64% of the infant cohort. The male/female ratio was reported in six studies.104, 182, 203, 262, 266, 268 The gender ratio of infants among different diet groups was evenly distributed in all of these studies.
In five studies most of the participants were White, accounting for 75% to 93% of the study population.104, 182, 227, 269, 270 Only one trial reported that Black infants comprised the majority of the study participants.203 Auestad et al.'s racial distribution of infants among the groups was not equal, for example, the breastfed group included significantly more White infants than the placebo group and the treatment groups.104 In two studies, participants were only White.205, 266 No information about the ethic/racial background of participants was provided in the remaining trials.
The inclusion and exclusion criteria were described in twelve studies.104, 182, 205, 227, 262–264, 266, 267, 269, 270 Only inclusion criteria were reported in one study.203 Four studies failed to report either inclusion or exclusion criteria.223, 260, 261, 268 Lapillonne et al. defined maternal cocaine and alcohol abuse history as exclusion criteria.267
The definition of a term infant (at least 37 weeks GA) was described in 11 studies 104, 223, 227, 260, 262, 263, 265, 266, 269, 270 The study duration ranged from 8 weeks to 24 months, with a mean interventional length of 27.5 weeks (range 8–52 weeks). Only one trial did not report the length of dietary intervention.261
Different variables were used to demonstrate the family socioconomic status across the studies (i.e., maternal education, paternal education, social score, social status of income earner, marital status). Maternal social status was determined in seven studies,205, 227, 262, 265, 268, 270 whereas, information about maternal and/or paternal education and/or maternal marital status was given in six trials.182, 205, 227, 265, 269 Makrides et al. assessed parental education scores, as well as parental social scores in two randomized study groups.266
There were no differences in sociodemographic variables among the study groups of randomized infants in all of these studies. Mothers of infants in the reference breastfed group had a more prestigious social score, and attained a higher level of education compared with mothers of formula-fed infants.205, 227, 262 Hoffman et al. found that maternal education was better in the LC PUFA supplemented group at baseline.270 There was missing data about maternal smoking history before and during pregnancy in eleven studies.104, 182, 203, 223, 262–265, 267, 269, 270 In studies that reported information about maternal smoking history, there was a tendency for less maternal smoking during pregnancy and/or lactation among the mothers of breastfed infants compared with formula-fed groups.205, 227, 266
Intervention/exposure characteristics. Only four studies reported as part of the protocol that the volume of formula consumed, calculated as the difference in the volume of formula in the bottle at the start and end of the feed, was recorded.203, 261, 265, 268 Nonetheless, most of the authors failed to report the daily amount of formulas consumed by infants in the different feeding groups. Only Decsi et al. reported that daily formula intakes were between 120 mL/kg and 150 mL/kg and did not differ between the feeding groups.261
The duration of formula intake was not reported only in the study of Decsi et al.261 In the remaining trials, the formula intake duration ranged from 8 weeks260 to 12 months.104, 205, 227
The sources of omega-3 FA intervention varied across the 18 RCTs. Six trials described the source as fish oil.104, 205, 227, 264, 267 Makrides et al. supplemented a standard formula with a combination of DHA derived from fish oil and AA derived from primrose oil.262 The specific type of fish from which the fish oil exposures were derived were described in two studies.104, 205 The remaining studies employed either single cell sources of FA,182, 268–270 solely vegetable sources of FA,203, 223, 260, 261, 263, 266 egg phospholipids,196, 265 or at least one of the feeding formulas containing FA from vegetable or egg sources.104, 205, 227, 264 Decsi et al. used a formula enriched with both egg lipids and primrose oil to achieve a higher levels of omega-3 and omega-6 FA.261
In 10 studies, the type of omega-3 FA employed included a combination of DHA and EPA.205, 223, 227, 261, 262, 264, 265, 267, 270 In four trials DHA was used alone;104, 182, 268, 269 ALA was used alone also in four trials.203, 260, 263, 266 Supplementation of formulas with the omega-6 FA AA was reported in seven trials.104, 182, 205, 227, 265, 269
Nine studies failed to report the name of the intervention formulas.104, 205, 227, 264–268 In the rest of the studies, the brands of the employed formulas were: Enfamil (Mead Johnson Nutritionals, Evansville, Ind);182, 203, 263, 269, 270 Similac with iron (Ross Laboratories, Columbus, OH);260 Aptamil (Milupa Ltd.);223 and Pre-Aptamil (Puch/Salzburg, Austria).261 Eight trials indicated the manufacturer of at least one omega-3 FA product used in their study.182, 223, 227, 265, 267, 269, 270 None of the studies reported on the purity of their omega-3 FA exposure.
Study infants were placed on the study formulas within the first week of life in most of the studies.104, 182, 205, 223, 260, 261, 265–268 Study formulas were started within the first month of life in four studies,203, 227, 263, 264 from the beginning of week 7 in the Birch et al. study,269 1 month after delivery in the study of Jorgensen et al.,264 and in the second Auestad et al. trial, infants received the formula after 3 months of being exclusively breastfed.227 One trial failed to report information on the exact time of participants' enrollment into the study.262 Hoffman et al.' infants were breastfed for at least 4 to 6 months and then were randomized to the study formulas until 12 months of age.270
Formula was the only source of alimentation in three studies and no solid foods were introduced during the entire trial period.203, 260, 263 Innis et al. specified that an infant would be withdrawn from the study if more than 10% of dietary energy came from sources other than assigned formula for 5 days or more.263 Decsi et al. permitted fruit juices at 2 months of age and solid food beginning at 3 months of age in both study groups.261 In eight studies, introduction of solid foods was permitted after 4 months of age.104, 205, 227, 262, 266, 267, 270 Both Birch et al. trials did not permit the introduction of any solid food until 17 weeks of age.182, 269 Lucas et al. reported that the mean age of first introduction of any solid food did not differ between those fed LCPUFA and those fed control formula.265 Two trials failed to report if any solid food was permitted at all.223, 268
Information about caloric balance of feeding formulas was reported in seven RCTs.104, 182, 227, 265, 269, 270 Only Auestad et al. mentioned that the study formulas were indistinguishable in appearance and odor.227
Cointervention characteristics. Three studies reported the content of vitamin and mineral supplements of feeding formulas and oils taken by pregnant or lactating women.182, 261, 264 In Ponder et al., no vitamins or mineral supplementations were given to the infants fed formula, whereas, breastfed infants received routine vitamin D supplementation.260 Only Jorgensen et al. reported about the use of preventive measures such as microencapsulation of fish and borage oils and addition of corn starch to avoid oxidation and to allow homogenization with the formula powder.264 Toxicology studies for supplemented oils were done only in one study.182
Outcome characteristics. Nine (of 20) trials evaluated the growth parameters as primary outcomes,120, 151, 324–329 while the remaining 11 trials assessed these outcomes as secondary outcomes. All included RCTs employed the weight, length, and HC of infants as main outcome measures for growth. The rate of gains in weight, length and HC were assessed in three studies.261, 264, 266 Triceps skinfold thickness was measured in five RCTs182, 203, 223, 268, 269 Subscapular skinfold thickness was assessed in five studies.182, 203, 265, 268, 269 Two studies evaluated mid-arm circumference as one of the growth outcomes.265, 268
| Study Quality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| A | B | C | ||||||||
| Applicability | I | Author | Year | n | Author | Year | N | Author | Year | n |
| AuestadA | 2001 | 239 | AuestadU | 1997 | 274 | InnisU | 1997 | 238 | ||
| AuestadA | 2001 | 165 | ||||||||
| II | Author | Year | n | Author | Year | N | Author | Year | n | |
| LucasA | 1999 | 447 | BirchU | 1999 | 79 | PonderU | 1992 | 43 | ||
| MakridesA | 2000 | 176 | WillattsU | 1998 | 40 | MakridesU | 1995 | 89 | ||
| BirchA | 2002 | 65 | MorrisU | 2000 | 140 | JensenU | 1997 | 80 | ||
| HoffmanA | 2003 | 68 | ||||||||
| III | Author | Year | n | Author | Year | N | Author | Year | n | |
| MakridesA | 1999 | 146 | DecsiU | 1995 | 22 | |||||
| JorgensenU | 1998 | 39 | ||||||||
| LapilloneU | 2000 | 24 | ||||||||
n = number of allocated/selected participants;
RCT = Adequate vs UUnclear allocation concealment; I Inadequate
The most frequently investigated outcomes across the included studies were infant weight, length, and HC, expressed as mean (SD), normalized z-score or gain over time.
Most of the studies failed to find a statistical difference between groups in the growth patterns at any time point. However, some differences were detected in five trials.
Only the study of Lapillonne et al. found that infants' HC at 4 months in the placebo group was significantly larger than that in both breast and treatment formula groups.267
Infant length and weight were not statistically different among the three feeding groups.267 Makrides et al., who compared growth parameters among three randomized groups, did not find statistically significant differences in weight, length, or HC at any age up to 2 years, even after adjusting for gender, GA, and postnatal age at assessment.205 When growth parameters were compared between the two treatment formula and the breastfed infant groups, investigators found that breastfed babies were significantly shorter and lighter than infants in the DHA+AA and DHA+EPA groups at 34 weeks and 12 months of age. These differences did not reach statistical significance at 2 years of age.205
Decsi et al., who randomized two groups of infants to receive either placebo or treatment formula, did not find a statistically significant difference between the groups regarding gain of weight, length, or HC at 4 months of age.261
The Makrides et at. study, which compared growth parameters in two randomized groups receiving placebo and treatment formulas, did not find any statistically significant difference in weight, length, or HC at 30 weeks of age.262
Three out of four RCTs describing the use of ALA as a source of omega-3 FAs, failed to find any significant difference in growth parameters among the randomized groups receiving either placebo or treatment formula(s). The weight, length, and HC of infants were similar at 4 and 8 weeks of age in the study of Ponder et al.,260 at 6, 16, and 34 weeks of age in the study of Makrides et al.266 and at 3 months of age in the Innis et al. study.263 Only one trial showed significantly lower weight at 120 days of age in the group of infants receiving the highest ALA intake, or the lowest LA/ALA ratio (LA [15.6wt%] and ALA [3.2wt%]), compared with the group receiving the lowest ALA, or highest LA/ALA ratio (LA [17.6wt%] and ALA [0.4wt%]).203 These results were obtained after adjusting for differences in birth weight, gender, and ethnicity. In Makrides et al.'s study, where newborn babies were randomized to receive formula with an LA:ALA of either 10:1 or 5:1, there were no significant differences in weight, length, and HC gain between the two groups, although breastfed infants had significantly lower weight and length gain at 16 and 34 weeks of age than infants in the two formula fed groups.266
Other growth outcomes assessed were triceps skinfold thickness, subscapular skinfold thickness, and mid-arm circumference. Five studies did not find a significant difference between groups in triceps skinfold thickness and subscapular skinfold thickness among the randomized study groups at any time point.182, 203, 223, 265, 269 Morris et al. randomized infants to receive either standard formula or the treatment formula with added DHA and found that subscapular skinfold thickness at 6 weeks and 3 months of age was significantly higher in the control group compared with the trial group, althought these differences were not evident at 6 months or at 1 year of age.268
Four studies measured the correlation between the plasma or RBC PUFAs and growth outcomes.203, 205, 262, 263 Two studies did not find a significant correlation between the omega-3 FA in plasma or RBC and the weight.203, 262 However, Jensen et al. observed a significant positive correlation between weight at 4 months and the plasma AA content at the same time.203 Innis et al., on the contrary, did not find a correlation between growth patterns and the plasma and RBC AA content in term infants.263
Makrides et al. found a significantly negative correlation between plasma DHA at 16 weeks and weight at 12 and 24 months of age.205
At 4 months of age, growth pattern outcomes were noted in 13 studies. However, only four studies included treatment groups of both DHA+AA and placebo.104, 182, 205, 227 For Auestad et al.'s first study,227 data on weight, length, and HC could not be extracted; although partially reported in the text for statistically significant differences, the sample sizes were not given, and the weight gains were reported in grams/day. The figure provided growth data by sex at different follow-up times, but no sample sizes were indicated. For the Birch et al. 1998 study,182 standardized weight and length were reported in a boxplot figure using z-scores, thus it was not possible to obtain unstandardized growth measures. This left only two studies for meta-analysis.104, 205 Both trials assessed the growth parameters as primary outcomes.
Meta-analysis was performed using the random effects weighted mean difference.
The WMD in the weight (kg) and length (cm) (DHA+AA vs. control) in two studies104, 205 was nonstatistically significant at 4 months. For weight: WMD: -0.06, CI 95%: -0.45; 0.34. For length: WMD: -0.33, CI 95%: -1.07; 0.40.
Meta-analysis was performed using the random effects weighted mean difference.
The WMD in the weight (kg), length (cm) and HC (cm) (DHA vs. control) in two studies104, 205 was nonstatistically significant at 4 months. For weight: WMD: -0.12, CI 95%: -0.44; 0.20. For length: WMD: -0.43, CI 95%: -1.20; 0.34. For HC: WMD: 0.04, CI 95%: -0.37; 0.46.
Meta-analysis was performed using the random effects weighted mean difference
The WMD in the weight (kg), length (cm) and HC (cm) (DHA+AA vs. control) in two studies104, 205 was nonstatistically significant at 12 months. For weight: WMD: -0.33, CI 95%: -0.87; 0.21. For length: WMD: -0.37, CI 95%: -1.26; 0.51. For HC: WMD: 0.14, CI 95%: -0.83; 1.12.
Meta-analysis was performed using the random effects weighted mean difference.
The WMD in the weight (kg), length (cm) and HC (cm) (DHA vs. control) in two studies104, 205 was nonstatistically significant at 12 months. For weight: WMD: -0.33, CI 95%: -0.87; 0.21. For length: WMD: -0.71, CI 95%: -2.18; 0.76. For HC: WMD: -0.04, CI 95%: -0.45; 0.38.
In most of the RCTs there was no evidence that randomization failed to produce comparable groups, with the exception of HC.268 In the study of Morris et al., two randomized groups had similar characteristics at recruitment, except for a small difference in mean HC which just reached statistical significance.268 In the study of Jorgensen et al., within the formula groups there was a borderline statistical difference in birth weight in favor of the group supplemented with only DHA.264 Jorgensen et al.264 and Auestad et al.227 also reported that maternal age of infants assigned to breast milk was significantly higher than that in the randomized formula-fed groups. In the study of Auestad et al., infants in the breastfed group also had a higher GA, a smaller percentage of mothers having no postsecondary education, and a smaller prevalence of smoking exposures both in utero and in the houshold.227
Four studies controlled the growth outcomes for potential confounders such as gender, maternal education, center, and socioeconomic status.203, 205, 263, 266 No differences were found after adjusting for these covariates.
The power calculation was reported in eleven trials,120, 124, 132, 151, 325, 329, 331, 333–335 while the intention-to-treat analysis approach was reported in only one study.132
| Author, Year, Location: Design | Study groups1 | Notable associations2,3 | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Guesnet, 1999, France: 6 wk parallel RCT143 | High-EPA (n=23)/ HM (n=15) | Low-EPA (n=24)/ pb (n=21) | S (-) correlation between Δ L & plasma & RBC EPA at birth | Jadad total: 2 [Grade: C]; Schulz: Unclear | III |
| Innis, 2001, Canada: prospective single cohort271 | Term breastfed infants (n=83) | n/a | RBC CPG DHA++ & EPG DHA+ negative correlation with infant weight (6 mo); no correlation at 12 mo; no correlation of blood AA & growth patterns at any age | Quality score: 8 [Grade A] | III |
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
N/A = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
RBC = red blood cells;
PL = phospholipid;
CPG = choline phosphoglycerides;
EPG = ethanolamine phosphoglycerides;
Δ = change;
L = length;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
↑ = increase;
↓ = decrease/reduction;
HM = human milk;
L = length
Guesnet et al. assessed growth patterns and their correlation with the plasma and RBC PUFA content after the use of three different formulas. Healthy term infants (n=68) were randomized to receive one of three formulas, supplemented with either DHA and EPA (high dose), DHA and EPA (low dose) or unsupplemented, for 6 weeks.143 It also included a group of infants who where breastfed, yet were nonrandomized. The formulas were provided by Gallia 1 (Bledina-sa, Groupe Danone, Villefranche-sur-saone, France).143
This study was conducted in France and supported by the Bledina-sa, Groupe Danon Paris, French Ministry of Cooperation in Mauritius and the University of Mauritius.
Blood samples were collected from umbilical cord at birth and venipuncture at 6 weeks of age. There was no difference between groups in the growth paramenters at 6 weeks of age.143
Innis et al. selected a cohort of 83 term infants who were exclusively breastfed, with birth weights ranging from 2,500 g to 4,500 g.271 The objective of the study was to measure the infant RBC DHA content and its association with visual, neuro or cognitive development.271 Infants were enrolled within 2 weeks of age and to be eligible, their mothers were required to intend to exclusively breastfeed their infant without providing infant formula or cow's milk for at least 3 months and without introducing solid foods for at least the first 4 months after birth. The infants were excluded if they had evidence of metabolic or physical abnormality, or if their mothers had substance abuse, metabolic or physiologic problems, or communicable diseases.271
Only one mother reported taking FA supplements with LA and DHA. The maternal diet was not reported or controlled. Only five mothers reported being smokers during the study. Infant measures of weight, length and HC were correlated with the RBC DHA and AA content at birth, 2, 4, 6, 9 and 12 months of age.271
Multiple linear regression analysis was used to determine the impact of the FA variables on the outcomes. The analysis controlled statistically for the duration of breastfeeding, maternal education, family income, gender, maternal smoking, birth order and birth weight, length and HC.271
Guesnet et al. observed a negative correlation between postnatal gains in length and the EPA concentration at birth in total plasma PL and in RBC PE.
Innis et al. found that the RBC choline phosphoglyceride (CPG) DHA and the ethanolamine phosphoglycerides (EPG) DHA, but not the plasma DHA, were significantly inversely related to infant weight at 6 months of age, but not at 12 months. There was no significant relation between infant blood lipid concentrations of AA and growth at any age.271
| Study Quality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| A | B | C | ||||||||
| Applicability | I | Author | Year | n | Author | Year | N | Author | Year | n |
| II | Author | Year | n | Author | Year | N | Author | Year | n | |
| III | Author | Year | n | Author | Year | N | Author | Year | n | |
| Innis | 2001 | 83 | GuesnetU | 1999 | 68 | |||||
n = number of allocated/selected participants;
= Unclear allocation concealment
| Author, Year, Location: Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Helland, 2001, Norway: 34 wks parallel RCT141 | Cod liver oil DHA+EPA (n=301) | Corn oil LA+ALA (n=289) | NS EEGs scores between groups (3 mo) | Jadad total: 4 [Grade: A]; Schulz: Unclear | III |
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
E-EPA = ethyl eicosapentaenoate;
n = sample size;
pts = study participants;
NR = not reported;
NS = nonsignificant statistical difference;
N/A = not applicable;
grp = group;
wk = week(s);
mo = month;
RBC = red blood cells;
PL = phospholipid;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
↑ = increase;
↓ = decrease/reduction;
EEG = electroencephalogram
Helland et al.,141 has been described in detail in the Pregnancy Outcomes and Growth Pattern Outcomes sections (see key questions: Duration of Gestation, Infants Small for Gestational Age, and Maternal Intake/Growth Patterns). A summary and the results relating to the current question are discussed here.
Helland et al. assessed the gestational length, birth weight, and neurologic and cognitive outcomes in a sample of 590 healthy pregnant women. They were randomized to receive 10 ml of cod liver oil (1,183 mg DHA, 803 mg EPA) or corn oil (LA and ALA) from week 18 of pregnancy to 3 months post delivery.141 They should not have taken any supplements of omega-3 FA earlier during the pregnancy. The exclusion criteria were premature births, birth asphyxia, infections, and anomalies in the infants that required special attention.141 The neurological outcomes assessed was the electroencephalogram (EEG) recordings of the included infants to evaluate brain maturity. EEGs were performed at 1 day of life and repeated at 3 months of age.141 Helland et al. had a high rate of dropouts, leaving 341 women in the final analysis (57%).288
There were no differences between groups in maturity as evaluated from the EEGs, neither at day 1 of life nor at 3 months of age.141
Between neonates with mature (score 1; n=70) and immature EEG scores (score 2 and 3; n=51), there were significant differences in umbilical plasma phospholipid levels of EPA, DPA and DHA at the 2nd day of life. At 3 months, there were no significant differences in plasma phospholipid levels between those with mature and immature EEGs.141
Study quality and applicability. Helland et al. received a Jadad total quality score of 4 (did not report method of double-blinding), indicating good internal validity. However, the allocation concealment was unclear. The applicability was scored with III, since the Norwegian population has a significantly higher intake of LCPUFA from marine sources compared to the Nort American population.
| Author, Year, Location: Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Gibson, 1997, Australia: 12 wk parallel RCT138 | 1.3 g/d DHA (n=8)/ 0.2 g/d DHA (n=10) | 0.9 g/d DHA (n=10)/ 0.4 g/d DHA (n=12)/ pb (n=12) | NS in PDI at 12 mo and 24 mo | Jadad total: 3 [Grade: B]; Schulz: Unclear | II |
| No correlation of sociodemographics & PDI at 1 y | |||||
| Positive correlation between level of education of partner & PDI+ | |||||
| Agostoni, 2001, Italy: Single prospective cohort284 | Term breastfed infants at 1 y-old (n=44) | n/a | NS correlation between Bayley's PDI & length of BF | Quality score: 8 [Grade A] | III |
| NS correlation between Bayley's PDI & milk FA content | |||||
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
E-EPA = ethyl eicosapentaenoate;
n = sample size;
pts = study participants;
NR = not reported;
NS = nonsignificant statistical difference;
N/A = not applicable;
grp = group;
wk = week(s);
mo = month;
RBC = red blood cells;
PL = phospholipid;
PDI = psychomotor developmental index;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
↑ = increase;
↓ = decrease/reduction;
BF = breast feeding;
PDI = Bayley's psychomotor scale
Gibson et al. was a double-blind RCT that investigated the effect of maternal intake of omega-3 FAs on breastfed infant's neurological and visual function outcomes in Australia.138 This study included mothers of term infants (>37 weeks of GA) who intended to breast feed for at least 12 weeks (n=52, means age: 30 [SD=4] years). These mothers were randomized to receive one of five doses of a DHA-rich algal oil (0, 0.2, 0.4, 0.9, 1.3 g DHA/day; DHASCO, Market Biosciences, MD, U.S.) between day 5 and week 12 postpartum. The oil contained 43% DHA, 1% omega-6 PUFA, 38% saturates and 18% monosaturates. Infants who were exclusively breastfed for 12 weeks were assessed. Infants (n=20) were healthy, appropriate weight for GA, and had Apgar scores greater than 7 at 5 minutes.138
Infant's visual function was assessed using visual evoked potentials (VEP) (logMAR) at 12 and 16 weeks of life.138 Global development (Bayley's Scales of Infant development) was assessed at 1 and 2 years of age. From Bayley Scales of Infant Development, the psychomotor developmental index (PDI) was derived. PDI assesses the control of gross and fine muscle groups, including walking, running, jumping, comprehension, use of writing implements, and imitation of hand movements. Mothers were from middle class families and completed year 12 of education. The five groups were compared in terms of maternal age, maternal BMI, GA, infant gender, birth weight, birth length, birth HC, Apgar score, siblings, maternal social score, smoking, education, home stimulation, and length of breast feeding, at baseline. There was a predominance of boys in the group that received the highest dose of DHA.138
Agostoni et al. evaluated the neurodevelopmental indices at 1 year of age in a single prospective cohort of term infants (n=44; 54.5% males) who were exclusively breastfed for at least 3 months in Italy.284 The children received breast milk for at least 3 months, after which weaning foods were introduced to all infants. Infants underwent clinical examination at 0, 1, 3, 6, 9 and 12 months of age.284
The mother's milk lipid composition was determined at each time-point. The day before, the control pooled milk was collected from all feedings over 24 hours. There was a progressive reduction of the number of breastfed infants to n=29 at 6 months, n=17 at 9 months and n=10 at 1 year.284
The mean PDI score was similar in infants between dietary groups at 1 and 2 years of age in Gibson et al. study.138 There were no associations with any sociodemographic variables at 1 year. The only association at 2 years of age was between PDI and the level of education of the partner (r 2=0.10; adjusted r 2=0.08, p<0.05).138
In Agostoni et al., the mean PDI in 1-year old infants, was 92 (SD=11.3).284 After correcting for potential confounders such us parity and mother's characteristics (i.e., age, education, smoking habits), breast feeding for 6 months or longer was not significantly correlated to the mean PDI result compared with subjects breastfed for 3 to 6 months (n=15).284 Associations between PDI and milk fat content and composition were measured with a multiple regression analysis. There was no correlation between PDI and the milk fat content at any time-point.284
Study quality and applicability. Gibson et al. obtained a Jadad total quality score of 3 (did not report methods of randomization and double-blinding), indicating sound internal validity.336 However, the allocation concealment was unclear. The applicability level was II for Gibson et al. and III for Agostoni et al.337
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Internal validity | Applicability | |
|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | ||||
| Bougle, 1999, France: 30 d parallel RCT254 | AA+EPA+ DHA formula (n=14) | LA (n-6)+ ALA (n-3) formula (n=11)/ HM (n=15) | NS LAEP between d 0 & 30d | Jadad total: 3 [Grade: B]; Schulz: Unclear | III |
| S↑ Δ motor NCT (m/s) in DHA/EPA/AA supplemented formula & HM from d0-30+ | |||||
| NS Δ sensory (m/s) test | |||||
| O'Connor, 2001, US, UK, Chile: 12 mo parallel RCT207 | DHA+AA (fish/fungal) (n=140)/ HM (n=43) | DHA+AA (egg-TG/fish) (n=143)/ Control formula (n=144) | (ITT) S↑ PDI score in <1250 g birth wt fed AA+DHA (egg-TG/fish) than control infants++ NS score control or AA+DHA (fish/fungal) groups | Jadad total: 3 [Grade: B]; Schulz: Unclear | I |
| van Wezel-Meijler, 2002, The Netherlands: 6 mo, parallel RCT272 | AA+DHA preterm formula (n=22) | Control formula (n=20) | S↑ PDI score unsupplemented group vs. supplemented formula at 3, 6, 12 & 24 mo+ | Jadad total: 5 [Grade: A]; Schulz: Adequate | III |
| Fewtrell, 2002, UK: 33 d parallel RCT273 | AA+DHA+EPA preterm formula (n=95) | Control formula (n=100)/ HM (n=88) | (ITT) NS PDI score between formula gps at 18 mo S ↑ PDI in the HM group vs. both formula gps | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
| NS between formula gps in KPSDSI at 9 mo; HM S ↑ quotient vs. formulas | |||||
| Clandinin, 2002, Canada: 92 wks parallel RCT193 | DAS (DHA+AA from SCO) (n=72)/ HM (n=105) | DAF (DHA from fish oils+AA from SCO) (n=90)/ Control formula (n=83) | S↑ PDI score formula gps (DAS, DAF) vs. control gp | Not assessed | X |
| Fewtrell, 2004, UK: 9 mo parallel RCT258 | GLA+ DHA formula (n=122) | Control formula (n=116) | (ITT) NS formula groups in Bayley's PDI scores at 18 mo | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acidLength = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
grp = group;
wk = week(s);
mo = month;
wt = weight;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
NCT = nerve conduction test;
LAEP = latency auditory evoked potentials;
SCO = single-cell oil;
HM = human milk;
TG = triglycerides
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Birch, 1992, US: 6 mo parallel RCT212 | Soy/marine oil: EPA+ DHA (n=26)/ HM (n=8) | Soy oil: ALA (n=22)/ Corn oil (n=18) | S↓ in VEP for all grps at 57 wks | S correlation between: RBC-DHA/DPA & VEP+++ | Jadad total: 2 [Grade: C]; Schulz: Unclear | II |
| S ↓ VEP in DHA+EPA vs. grps 2–3 at 36–57 wks+ | RBC-DHA/DPA & FPL+ at 57 wks | |||||
| NS b-Rod ERG at 36–57 wks | ||||||
| Carlson, 1992, US: 12 mo parallel RCT185 | Marine oil: DHA + EPA (n=33) | Control: LA (n=34) | S ↑ resolution acuity in DHA +EPA vs. control at 2 & 4 mo +++ | S correlation (+) RBC DHA at 2 mo with visual acuity at 2,4 mo | Jadad total: 4 [Grade: A]; Schulz: Adequate | II |
| Koletzko, 1995, Germany: 21 d parallel RCT251 | LCPUFA-enriched: DHA + EPA + ALA (n=9) | Control: (n=10)/ HM (n=8) | NS difference in visual acuity across at 21 d | n/a | Jadad total: 2 [Grade: C]; Schulz: Unclear | III |
| Carlson, 1996, US: 4 mo parallel RCT191 | Marine oil: DHA +EPA (n=26) | Control ALA (n=23) | S↑ higher acuity in DHA+EPA vs. control at 2 mo+ NS at 4–12 mo | n/a | Jadad total: 3 [Grade: B]; Schulz: Unclear | II |
| Faldella, 1996, Italy: 5 mo parallel RCT198 | LCPUFA-enriched: DHA +EPA+ ALA (n=21) | Control EPA + ALA (n=25)/ HM (n=12) | S shorter wave (N4 & P4) latencies VEP in DHA+EPA vs. control at 52 wks PCA++ | At 52 wks PCA, inverse correlation between: RBC-DHA & N4 wave latency + & RBC-DHA & P4 wave latency++ | Jadad total: 1 [Grade: C]; Schulz: Unclear | III |
| NS in BAEP & ERG (a & b) latencies) across grps1–3 | ||||||
| Bougle, 1999, France: 30 d parallel RCT254 | LCPUFA-enriched: DHA + EPA + ALA (n=14) | Control (n=11)/ HM (n=15) | NS in VEP (N1 wave latency) at 30 d | n/a | Jadad total: 3 [Grade: B]; Schulz: Unclear | III |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
wt = weight;
RBC = red blood cells;
PL = phospholipid;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase;
↓ = decrease/reduction;
HM = human milk;
GA = gestational age;
PCA = postconception age;
CA = corrected age;
ERG = electroretinogram;
BAEP = brainstem acoustic evoked potential
Study characteristics. Six parallel RCTs involving preterm infants were identified to address these questions.193, 207, 254 258, 272, 273 Five of the studies were published in English scientific journals, while one was published as an abstract.193 Bougle et al.'s study was conducted in France,254 both Fewtrell et al.'s studies were conducted in the U.K.,258, 273 the van Wezel-Meijler et al. study was located in the Netherlands,272 Clandinin et al.'s study was conducted in Canada,193 and the O'Connor et al. study took place in the United States, United Kingdom and Chile.207
Three studies involved three study arms comparing the use of supplemented and unsupplemented infant formula with the addition of a fourth reference standard group (i.e., human milk).193, 207, 254 Two RCTs compared only two study groups (i.e., formula with or without LCPUFA),258, 272 whereas, another study also included a group using human milk as a reference standard.273
van Wezel-Meijler et al.272 and Fewtrell et al. (2002)273 were supported by a private source (Numico Research). Clandinin et al. was funded by Mead Johnson & Company (pharmaceutical-nutritional company),193 whereas, Fewtrell et al. (2004)258 was supported by H.J. Heinz Company (food company). O'Connor et al. and Bougle et al. did not report their funding source.207, 254
Population characteristics. There were 1,228 preterm infants enrolled across the included studies that were randomized to receive the supplemented or control formulas. The sample sizes ranged from 25 to 470 participants. The mean age of the infants at randomization was not significantly different between study groups across five RCTs.207, 254, 258, 272, 273 Clandinin et al. did not report the age of their infants.193 The GA of the preterm infants was below 37 weeks across five studies,207, 254, 258, 272, 273 except for Clandinin et al. that also included VLBW term infants.193 The between-group difference in GA was not significant across the studies.
In four studies, the proportion of male participants did not differ significantly between randomized groups,207, 258, 272, 273 although two studies did not mention this information in their report.193, 254 The range of males varied between 35%272 to 56%.207
O'Connor et al. was the only one to describe the racial composition of their participants, which was predominantly White.207 The rest of the studies failed to provide the race and/or ethnicity of their subjects.
Other variables like birth weight, proportion of SGA infants, percentage from multiple pregnancies, and Apgar score at birth, were nonstatistically different between groups in O'Connor et al.207 van Wezel-Meijler et al. matched their population by birth weight and proportion of SGA at baseline.272 Infants in both of Fewtrell et al.'s studies were well matched by birth weight and length, proportion of SGA, proportion from multiple pregnancies, and delivery by C-section at baseline.258, 273
Three of six studies analyzed the between-group difference of maternal covariates. O'Connor et al. matched their study groups by maternal age, education, smoking status during pregnancy and in the home, prenatal care, the HOME inventory score and maternal intelligence measured with WAIS-R Raw vocabulary score.207 The HOME Inventory Score was statistically different depending of the birth weight group—in infants <1,250 g, the control group had a higher score than infants in the AA+DHA (fish/fungal) group and in infants >1,250 g, the control group had a higher score than the AA+DHA (egg-TG/fish) group. Finally, the infants with a birth weight higher than 1,250 g in the AA+DHA (fish/fungal) group had a higher score than those in the AA+ DHA (egg-TG/fish) group.207
The inclusion criteria were described in every included study, however, exclusion criteria were not reported in two studies.193, 273
The studies included mostly healthy preterm infants with a defined range of weight drawn from neonatal intensive care units (NICU). Bougle et al. included healthy preterm infants (<34 weeks GA) free of respiratory, metabolic or neurological disease.254 O'Connor et al. selected preterm infants (<33 weeks GA) with a birth weight ranging from 750 g to 1,805 g, including singleton and twin births as well as SGA subjects, that could initiate enteral feeding by the 28th day of life.207 van Wezel-Meijler et al. included premature infants (<34 weeks GA) with birth weight of <1,750 g, normal neurological examination throughout the neonatal period, normal repeated brain ultrasound or showing minor abnormalities such as isolated subependymal haemorrhage and subventricle, with no ventricular dilation, transient periventricular echodensities, without evolution into cysts or any combination of previous findings.272 Infants in the Fewtrell et al. (2002) trial had a GA below 37 weeks and a birth weight of <1,750 g, were free of congenital malformations known to affect neurodevelopment, and whose mothers decided not to breastfeed at 10 days of age.273 Fewtrell et al.'s (2004) preterm infants (GA <35 weeks) with birth weight ≤2,000 g received at least one of their enteral feeds as formula milk during their hospital stay.258 On the other hand, Clandinin et al. included VLBW term and preterm infants after their feeding reached 30 mL/kg/day.193
Three studies excluded infants with serious congenial abnormalities affecting growth and development, major surgery before randomization, perivenricular or intraventricular hemorrhage, maternal incapacity, liquid ventilation asphyxia resulting in severe and permanent neurologic damage, or uncontrolled systemic infection at the time of enrollment.207, 258, 272
The baseline characteristics of the patients in the Bougle et al. study were nonstatistically significant for the electrophysiological studies (i.e., motor and sensory nerve conduction studies, auditory evoked potentials).254
Only three trials measured the blood content of FAs at baseline.207, 272 O'Connor et al. found a nonsignificant difference between groups in the plasma or RBC (lipid fractions) levels of AA and DHA.207 van Wezel-Meijler et al. observed the same finding.272 Bougle et al.'s plasma phospolipid composition of EPA was significantly lower in the low LCPUFA supplemented formula than in the DHA/EPA/AA supplemented formula and human milk.254 However, the RBC content of omega-3 and omega-6 did not differ between groups. The Bougle et al. study was the only one to describe the FA content in human milk i.e., 0.5% (SD 0.1) total FA DHA and ALA (omega-3) plus 0.9% (SD 0.2) total FA AA.254
None of the studies reported the presence of concurrent conditions in the study population and/or the use of medications. However, van Wezel-Meijler et al. reported that 13 patients were excluded from the analyses for the following reasons: necrotizing enterocolitis (n=2, 1 each group); chronic lung disease (n=3; n=2 DHA-AA vs n=1 control); grade 4 retinopathy of prematurity (n=1 AA+DHA); cystic periventricular leucomalacia (n=1 control); and, duration of artificial ventilation at baseline.272 No differences were found between groups.272 None of the studies included information regarding maternal concurrent conditions, medications or background diet, that could be relevant for the infants consuming breast milk.
No other pre-study medications or treatments were mentioned in the included studies. The infants in the O'Connor et al. study were formula and/or human milk fed before study entry,207 whereas, van Wezel-Meijler et al.'s infants received parenteral nutrition using glucose/Vaminolact 6.75%/Intralipid 20% (Kabi-Fresenius, Stockohlm, Sweden) for an average of 12 to 17 days, from 24 hours after birth.272 This parenteral nutrition contained negligible amounts of LCPUFA. Three to 7 days after birth, enteral feeding was introduced using preterm formula (without LCPUFA). Total enteral nutrition was usually achieved within 2 to 3 weeks after birth.272
Intervention/exposure characteristics. The intervention groups in each trial received different types of supplemented infant formula, therefore, each study will be discussed separately.
Bougle et al.'s small sample were randomized to receive a formula with 17.7% total FA of LA (omega-6), AA (0.1%), ALA (omega-3: 1.2%), EPA (0.1%) and DHA (0.6%), for at least 30 days.254
O'Connor et al. randomized their participants to receive one of three study formulas with or without the addition of LCPUFA until term CA. The intra-hospital preterm formula was a modified version of Similac Special Care ready-to-feed (Ross Products Division, Columbus, OH, U.S.) with or without AA- and DHA-enriched oils. At term CA, postdischarge nutrient-enriched formula (modified version of NeoSure powder) with and without the same sources of AA+DHA and/or human milk was given to the infants until 12 months CA.207 The first group received a supplemented formula with fungal and low-EPA fish oil (DHA/EPA ratio: 3.5/1) providing 0.27 g DHA, 0.08 g EPA and 0.43 g AA (per 100 mL) in the Similac Special Care formula and 0.16 g DHA and 0.43 g AA in the NeoSure formula. In the other group, egg-tryglyceride (TG) and low-EPA fish oil provided 0.24 g DHA and 0.41 g AA to the Similac formula, but 0.15 g DHA to NeoSure. The purveyors of the fish, fungal and egg-TG oils were Mochida International (Japan), Suntory Ltd. (Japan) and Eastman Chemicals Co (U.S.), respectively. The duration of the treatment was until 12 months CA.207
In van Wezel-Meijler et al., the neonates were randomized to receive preterm liquid formula supplemented with (4.4 g/100mL fat) a 2/1 ratio of DHA (0.015 g/100mL [0.34% fat]) as DHASCO® oil produced by microalgae (Martek Inc., Columbia, U.S.) and AA (0.031 g/100 mL [0.68% fat] as ARASCO® oil produced by fungi (Martek Inc.). The formula was continued from enrollment until a weight of 3000 g was reached. Subsequently, this group continued with a supplemented term formula (3.5 g/100 mL fat) with a reduced absolute amount of DHA (0.012 g/100 mL; 0.34% fat) and AA (0.025 g/100 mL; 0.70 % fat) until 6 months CA.272
Fewtrell et al. used a LCPUFA-supplemented preterm formula (n=95) (Prematil, Milupan) with fat blended from vegetable oils (palm coconut, soya, sunflower) and milk fat with derivates of LA and ALA sourced from evening primrose oil (GLA) and egg-lipids (AA [0.31 g/100 mL, DHA [017 g/100 mL], EPA [0.04 g/100mL]). Formula was provided as a ready-to-feed form for a mean of 31 days until neonatal unit care discharge.273
Clandinin et al. included two interventional groups. The first group (DAS group) received 17 mg DHA plus 34 mg AA/100 Kcal from single cell oils (SCO) (n=72) as preterm formula (24 Kcal oz), discharge formula (22 Kcal oz) and term formula (20 Kcal oz). The second group (DAF group) received the same formula as the DAS group but with 17 mg DHA/100 Kcal from fish oil and 34 mg AA/100 Kcal from single cell oils (n=90).193
Fewtrell et al.'s study 2004 study used a preterm infant formula supplemented with LCPUFA (OsterPrem with LCPUFA) until the infants were discharged from the NICU. Afterwards, a nutrient-enriched postdischarge formula was used (Farley's PremCare with LCPUFA). The fat was a blend of vegetable oils (high oleic sunflower oil, palmolein, palm kernel oil, and canola oil). LCPUFAs were sourced from borage (starflower) oil (GLA [omega-6] 0.9 g/100 mL) and tuna fish oil (high DHA/EPA ratio: DHA 0.5 g/100 mL, EPA 0.1 g/100 mL, AA: 0.04 g/100 mL). Formula was provided in ready-to-feed form during the hospital stay and in powdered form after discharge up to 9 months after CA.258
The studies compared the interventional formulas with unsupplemented infant formulas that were identical in appearance and smell,258, 273 contained the same proportion of monosaturated and saturated FAs, and given to the infants during the same period of time as the intervention group. Bougle et al. compared the supplemented formula with a LA (omega-6) and ALA (omega-3) enriched formula.254
The studies did not provide information regarding background diet, when introduced, and the purity data the omega-3 supplements. No study report included details as to whether, or how, the presence of methylmercury was tested for, or eliminated from, the omega-3 FA exposure.
Cointervention characteristics. Human milk was the reference standard group, either as a separate arm193, 258, 273 or as part of the formula groups that did not comply with the intervention.207 Bougle et al permitted the use of supplements, which contained dextrines, proteins and minerals during the study period. The patients received daily supplementation with 1,200 IU of vitamin D and 4.5 mg of vitamin E (Uvesterol ADEC).254 Infant preterm and term formulas in the O'Connor et al. study contained beta-carotene and natural vitamin E.207 Participants in both of Fewtrell et al.'s studies received an identical proportion of minerals and vitamins (A,D,E,K) in their formulas.258, 273
Outcome characteristics. Only one study performed electrophysiological studies at baseline and after treatment.254 This study measured the latencies of auditory evoked potentials (BAEP test), motor and sensory nerve conduction studies on the posterior tibial nerve and the flexor hallucis brevis muscle.254
The Bayley's PDI was assessed in five of six studies.193, 207, 258, 272, 273 O'Connor et al.'s average percent of agreement on scoring between site testers and central testers was 93% (range: 73%-100%).207
The first Fewtrell et al. study utilized the Knobloch, Passamanick and Sherrard's Developmental Screening Inventory (five subscales: adaptative, gross motor, fine motor, language and personal-social) to assess neurodevelopment at 9 months, as well as neurologic impairement at 9 and 18 months of followup (diagnosed by examining pediatrician).273
| Study Quality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| A | B | C | ||||||||
| Applicability | I | Author | Year | n | Author | Year | n | Author | Year | n |
| II | Author | Year | n | Author | Year | n | Author | Year | n | |
| III | Author | Year | n | Author | Year | n | Author | Year | n | |
| Matorras | 1994 | 69 | Vilbergson | 1991 | 33 | |||||
| Rump | 2001 | 627 | Elias | 2001 | 84 | |||||
| Cetin | 2002 | 21 | ||||||||
n = number of allocated/selected participants
The latencies of auditory evoked potentials (i.e., Wave I, Wave III, Wave V and I-V interpeak latency) difference between day 0 and day 30 were not significant in the study of Bougle et al.254 The change in the motor nerve conduction test (m/s) was significantly higher in the group receiving the DHA/EPA/AA-supplemented formula and in the human milk groups, from day 0 to day 30. However, the change in the sensory test (m/s) was nonsignificant during the same period.254
Five studies evaluated Bayley's PDI after the administration of supplemented formula, unsupplemented formula, and/or human milk only (reference standard).193, 207, 258, 272, 273 In O'Connor et al., a statistically significant feeding by birth weight stratum interaction was observed for Bayley PDI (p=0.005) among infants who consumed >80% of their feeding as study formula and/or human milk.207
van Wezel-Meijler et al. observed a statistically significant higher PDI score for the unsupplemented group compared with supplemented formula group, at 3, 6, 12 and 24 months.272 The first Fewtrell et al. study did not find a statistical difference between formula groups at 18 months. Although the human milk group was not randomized, since it was used as reference standard, the PDI was significantly higher in the breastfed group compared with both formula groups.273
Clandinin et al., using ANOVA analysis, found that the control group had a significantly lower PDI score than the formula groups (DAS, DAF) and the human milk group (reference standard).193 The second Fewtrell et al. study showed that there was a nonstatistical diference in Bayley's PDI scores between formula groups at 18 months.258
Fewtrell et al. found that The Knobloch, Passamanick and Sherrard's Developmental Screening Inventory scores (quotient) at 9 months did not differ significantly between the formula groups, whereas, the breastfed group had a significantly higher quotient compared with the formula groups.273 This study also failed to find a difference in neurological impairment between formula groups, at 9 and 18 months of followup.273
Bougle et al.'s cohort of healthy preterm infants had seven dropouts during the study. The main reasons were NEC (n=1) in the human milk group, hydrocephalus in the control formula group (n=5), and transfer to their referring hospital (n=3 human milk group, n=1 control, n=1 supplemented formula group).254
O'Connor et al.'s had 94 withdrawals (80%) at 12 months CA.207 There was no statistical difference in the number of withdrawals between groups. The main reason for withdrawals was symptoms related to feeding intolerance. During the study 6 infants in the control group, 3 in the AA+DHA (fish/fungal) group, 6 in the AA+ DHA (egg-TG/fish) group, and none in the human milk groups, died. None of the infant deaths were related to study feedings.207
There were 13 dropouts in the van Wezel-Meijler et al. study.272 Reasons for withdrawal were: necrotizing enterocolitis; chronic lung disease; grade 4 retinopathy of prematurity; cystic periventricular leucomalacia; change from formula feeding to mother's expressed milk; and, home-to-hospital distance. There were no losses to followup.272
In the first Fewtrell et al. study, six patients randomized to the control formula withdrew from the trial before 3 weeks for the following reasons: early discharge (<3 weeks of age; n=3); necrotizing enterocolitis (n=1); intolerance of feeds (n=1); and, breastfed (n=1).273 Fourteen infants withdrew in the supplemented formula group. Reasons for withdrawal were: early discharge (n=2); necrotizing enterocolitis (n=5); maternal concern (n=2); and, death(n=2).273 There were 14 lost to follow up at 9 months in the control group, whereas, only one infant withdrew in the supplemented formula group and three in the human milk group. There were two deaths in the supplemented formula group and three in the human milk group.273 Clandinin et al. failed to report the dropouts.193 Fewtrell et al.'s reasons for dropouts were: in the control group—abdominal distention (n=1); death due to bronchopulmonary dysplasia at 25 days of age (n=1); and lost to follow up at 18 months (n=21).258 In the supplemented formula group, the reasons for dropouts were: necrotizing enterocolitis (n=1); and, lost to follow up at 18 months (n=15).258
The inclusion criteria for meta-analysis in this population were: 1. Formula with same content of omega-3 FA supplements (e.g., DHA+ AA or DHA alone) compared with a control formula without omega-3 FA; 2. same outcome measure; 3. same follow-up period or timepoint of outcome measure; 4. at least two trials. Only five studies measured the Bayley's Developmental Index (PDI). This outcome was chosen to evaluate the possibility of meta-analysis. However, outcome results were only available for more than one study at two follow-up times: CA 12 months and 18 months. At 12 months CA, outcomes were available for two studies.207, 272 In Wezel-Meijler et al.,272 the experimental group received supplemented formula from the first enteral feeding time until 6 months CA. In O'Connor et al.,207 however, supplemented formula was used until 12 months CA. We would have combined data at 6 months follow-up, however, this data was not available in O'Connor et al.207 Thus, meta-analysis was not possible for this outcome.
O'Connor et al.'s Bayley's PDI score in <1,250 g birth weight infants who strictly followed the feeding protocol was greater in infants fed AA+DHA (egg-TG/fish) than control infants, even after adjusting for a number of covariates including the HOME inventory, maternal WAIS-R, and human milk intake.207 The score did not differ statistically from either the control or AA+DHA (fish/fungal) groups. In an ITT and subgroup population analysis, the percentage of participants who had a significantly delayed motor performance did not differ statistically by study formula group.207
In van Wezel-Meijler et al., after adjusting for birth weight and number of SGA infants, there was no difference in PDI between the groups.272
To explore the possible influence of maturity on the response to LCPUFA supplementation, the first Fewtrell et al. study stratified the cohort by GA (<30 weeks). Infants who had a GA <30 weeks and received LCPUFA supplemented formula, had a Bayley PDI of 5.8 points higher than the control group, although the difference was nonsignificant.273 There were no differences in Bayleys PDI between supplemented and control groups with a GA >30 weeks.273 In this study, there was no significant interaction between formula and duration or volume of formula consumed on later outcome. At 18 months of age, breastfed infants had a significantly higher PDI score than formula groups. This result persisted after adjusting for effect modifiers (social class, level of maternal education, birth order and marital status).273
The second Fewtrell et al. study did not find a significant difference between groups when the PDI scores were adjusted by gender, GA and birth weight.258
The remaining studies did not report on the control for effect modifiers.
The power calculation was reported in three trials,310, 321, 322 while the intention-to-treat analysis approach was reported in both Fewtrell et al.'s trials.321, 322
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Agostoni, 1995, Italy: 4 mo Parallel RCT176 | DHA+ EPA+ AA formula (n=27) | Control formula (n=29)/ HM (n=30) | S better score in DHA+EPA in Brunet-Lezine test (DQ) at 4++ | RBC DHA at 4 mo S + correlation with DQ at 4 mo NS at 24 mo | Jadad total: 4 [Grade: A]; Schulz: Unclear | II |
| NS at 24 mo | NS at 24 mo | |||||
| Auestad, 1997, US: 12 mo parallel RCT104 | Formula DHA+AA (n=46)/ HM (n=63) | Formula DHA (n=43)/ control formula (n=45) | S better in control gp vs. DHA+AA in PDI at 12 mo | n/a | Jadad total: 3 [Grade: B]; Schulz: Unclear | I |
| NS among 3 gps | ||||||
| Lucas, 1999, UK: 6 mo parallel RCT265 | Formula LCPUFA (n=154) | control formula (n=155)/ HM (n=138) | NS in PDI at 18 mo; NS in KPS at 9 mo (ITT) | n/a | Jadad total: 5 [Grade: A]; Schulz: Adequate | II |
| Birch, 1998, US: 17 wk parallel RCT182 | Formula DHA+AA (n=27) | Formula DHA (n=26)/ NR pb (n=26) | NS in PDI at 18 mo; NS in BRS at 18 mo | NS correlation of PDI & BRS at 18 mo and plasma & RBC LA, ALA, AA, EPA, or DHA at 4 mo & 12 mo | Jadad total: 5 [Grade: A]; Schulz: Unclear | I |
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA; n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
ALA = linolenic acid;
LA = alpha linoleic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
HM = human milk group;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = statistically significant difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
wt = weight;
PDI = psychomotor developmental index, Bayley scale;
KPS = Knobloch, Passmark, and Sherrard's test;
BRS = behavioral rating scales;
RBC = red blood cells;
ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
DQ = developmental quotien;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001
| Author, Year, Location: Length & Design | Study groups1 | Notable clinical effects | Notable clinical-biomarker2,3 correlations | Internal validity | Applicability | |
|---|---|---|---|---|---|---|
| Group 1 (n)/ Group 4 (n) | Group 2 (n)/ Group 3 (n) | |||||
| Makrides, 1999, Australia: 12 mo parallel RCT205 | Formula DHA+AA (n=28)/ NR HM (n=63) | Formula DHA (n=27)/ NR pb (n=28) | NS in PDI at 12 & 24 mo | S correlation between PDI at 12 mo & plasma AA levels at 12 mo | Jadad total: 5 [Grade: A]; Schulz: Adequate | III |
| Auestad, 2001a, US: 12 mo parallel RCT227 | DHA+ AA (egg-TG) formula (n=80) | DHA+ AA (fish/fungal) formula (n=82)/ control formula (n=77) | NS in PDI at 6 & 12 mo | n/a | Jadad total: 5 [Grade: A]; Schulz: Adequate | I |
| Auestad, 2001b, US: 1 y, parallel RCT227 | DHA + AA formula/ HM (n=83) | Control formula/ HM (n=82) | NS in PDI at 6 & 12 mo | n/a | Jadad total: 5 [Grade: A]; Schulz: Adequate | I |
| Jensen, 1997, US: 120 d parallel RCT203 | Formula 1 LA/ALA 44/1 (n=20)/ F 3 LA/ALA 9.7/1 (n=20) | Formula 2 LA/ALA 18.2/1 (n=20)/ F 4 LA/ALA 4.7/1 (n=20) | NS in PDI at 12 mo | S correlation between plasma DHA & PDI | Jadad total: 2 [Grade: C]; Schulz: Unclear | II |
| S ↓ score (Gross motor DQ) in F 1 & F 3 vs. F2 & 4+ | NS correlation between RBC DHA & PDI | |||||
Proceeding from highest omega-3, or lowest omega-6/omega-3, fatty acid content of intervention/exposure;
biomarker source;
biomarkers = EPA, DHA, AA, AA/EPA, AA/DHA, AA/EPA+DHA;
n-3 = omega-3 fatty acids;
n-6 = omega-6 fatty acids;
LA = linolenic acid;
ALA = alpha linolenic acid;
DHA = docosahexaenoic acid;
EPA = eicosapentaenoic acid;
AA = arachidonic acid;
HM = human milk group;
Length = intervention length;
Design = research design;
n = sample size;
pts = study participants;
NR = not reported;
S = significant statistical difference;
NS = nonsignificant statistical difference;
n/a = not applicable;
pb = placebo;
grp = group;
wk = week(s);
mo = month;
PDI = psychomotor developmental index, Bayley scale;
CLOG = cod liver oil group;
COG = corn oil group;
RBC = red blood cells;
p<.05 or significant with 95% confidence interval;
p<.01;
p<.001;
p<.0001; ITT = intention-to-treat analysis;
PP = per-protocol analysis (e.g., completers);
↑ = increase(d)/higher;
↓ = decrease(d)/reduction/lower;
DQ = developmental quotien
Study characteristics. All studies were parallel RCTs with at least two arms. Countries where the studies were conducted included the United States,104, 182, 203, 227 Italy,176 Australia,205 and the U.K.265
Agostoni et al. did not report their funding source.176 Auestad et al.'s104 study was supported by Ross Products Division, Abott Laboratoris, Columbus, OH and the U.S. Maternal and Child Health Bereau, Rockville, MD. Lucas et al.'s study was funded by Nestec Ltd (Switzerland).265 The study of Birch et al. was supported by an NIH grant and Mead Johnson Nutritional Center (Evansville, IN).183 Makrides et al.'s study was sponsored by Nestec Ltd (Switzerland), the MS McLeod Research Trust and the Australian National Health and Medical Research Council.205 Both of Auestad et al.'s trials were supported by Ross Products Division, Abott Laboratoris, Columbus, OH.227 The study of Jensen et al. was sponsored by federal funds from the U.S. Department of Agriculture, Agricultural Research Service.203
Population characteristics. Maternal and infant characteristics were analyzed separately. Across the seven RCTs, sample sizes ranged from 60176 to 447265 infants. The maternal sample size was provided in only one study.265
The definition of a term infant (at least 37 weeks GA) was described in seven studies.104, 176, 182, 205, 227, 265
Of eight RCTs, the mean GA of randomized infants was reported in six studies and ranged from 39 to 40.3 weeks).176, 203, 205, 227 The percentage of males of randomized infants was reported in five studies and ranged from 46.4% to 52.5% of infants.176, 182, 205, 227
The gender ratio of the infants, among the different diet groups, was evenly distributed in four studies;176, 182, 227 however, in the study of Makrides et al., there was a tendency for proportionally more boys to be enrolled in the group that received the highest dose of DHA.205
The mean age of the infant's mothers across the ei
