Format

Send to

Choose Destination
Am J Clin Nutr. 2017 Dec;106(Suppl 6):1694S-1702S. doi: 10.3945/ajcn.117.156075. Epub 2017 Oct 25.

U-shaped curve for risk associated with maternal hemoglobin, iron status, or iron supplementation.

Author information

1
Program in International and Community Nutrition and Department of Nutrition, University of California, Davis, CA kgdewey@ucdavis.edu.
2
Program in International and Community Nutrition and Department of Nutrition, University of California, Davis, CA.

Abstract

Both iron deficiency (ID) and excess can lead to impaired health status. There is substantial evidence of a U-shaped curve between the risk of adverse birth outcomes and maternal hemoglobin concentrations during pregnancy; however, it is unclear whether those relations are attributable to conditions of low and high iron status or to other mechanisms. We summarized current evidence from human studies regarding the association between birth outcomes and maternal hemoglobin concentrations or iron status. We also reviewed effects of iron supplementation on birth outcomes among women at low risk of ID and the potential mechanisms for adverse effects of high iron status during pregnancy. Overall, we confirmed a U-shaped curve for the risk of adverse birth outcomes with maternal hemoglobin concentrations, but the relations differ by trimester. For low hemoglobin concentrations, the link with adverse outcomes is more evident when hemoglobin concentrations are measured in early pregnancy. These relations generally became weaker or nonexistent when hemoglobin concentrations are measured in the second or third trimesters. Associations between high hemoglobin concentration and adverse birth outcomes are evident in all 3 trimesters but evidence is mixed. There is less evidence for the associations between maternal iron status and adverse birth outcomes. Most studies used serum ferritin (SF) concentrations as the indicator of iron status, which makes the interpretation of results challenging because SF concentrations increase in response to inflammation or infection. The effect of iron supplementation during pregnancy may depend on initial iron status. There are several mechanisms through which high iron status during pregnancy may have adverse effects on birth outcomes, including oxidative stress, increased blood viscosity, and impaired systemic response to inflammation and infection. Research is needed to understand the biological processes that underlie the U-shaped curves seen in observational studies. Reevaluation of cutoffs for hemoglobin concentrations and indicators of iron status during pregnancy is also needed.

KEYWORDS:

anemia; ferritin; iron deficiency; iron supplementation; low birth weight; pregnancy; preterm birth; small-for-gestational age; soluble transferrin receptor; stillbirth

PMID:
29070565
PMCID:
PMC5701708
[Available on 2018-12-01]
DOI:
10.3945/ajcn.117.156075
[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Silverchair Information Systems
Loading ...
Support Center