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WMJ. Author manuscript; available in PMC 2009 March 3. Published in final edited form as: WMJ. 2008 November; 107(7): 320–326. | PMCID: PMC2650395 NIHMSID: NIHMS89793 |
A comparison of Wisconsin Neonatal Intensive Care Units with National data on outcomes and practices Erika W. Hagen, PhD,1 Mona Sadek-Badawi, MBBCH,1 Aggie Albanese, BS,1 and Mari Palta, PhD1,2 1Department of Population Health Sciences, University of Wisconsin, Madison 2 Department of Biostatistics and Medical Informatics, University of Wisconsin, Madison Context: Improvements in neonatal care over the past three decades have resulted in increased survival of infants at lower birthweights and gestational ages. However, outcomes and practices vary considerably between hospitals. Objective: To describe maternal and infant characteristics, NICU practices, morbidity, and mortality in Wisconsin neonatal intensive care units (NICU) and to compare outcomes in Wisconsin to the National Institute of Child Health and Human Development network of large academic medical center NICUs. Design and Setting: The Newborn Lung Project Statewide Cohort is a prospective observational study of all very low birthweight (≤ 1500 grams) infants admitted during 2003 and 2004 to the 16 level III NICUs in Wisconsin. Anonymous data were collected for all admitted infants (N=1463). Main outcome measures: Major neonatal morbidities, including bronchopulmonary dysplasia, intraventricular hemorrhage, necrotizing enterocolitis, and retinopathy of prematurity were evaluated. Results: The overall incidence of bronchopulmonary dysplasia was 24% (range 8-56% between NICUs); intraventricular hemorrhage incidence was 23% (9-41%); the incidence of necrotizing enterocolitis was 7% (0-21%); and the incidence of grade III or higher retinopathy of prematurity was 10% (0-35%). Conclusion: The incidence rates of major neonatal morbidities in Wisconsin were similar to those of a national network of academic NICUs. The Newborn Lung Project is a unique regional cohort of very low birthweight (VLBW, ≤1500 grams) children based on births in Wisconsin. This study, started in 1987, has followed up on health, behavior, and academic outcomes of cohort children for almost two decades. The first cohort includes all VLBW children admitted to six Neonatal Intensive Care Units (NICU) between 1988 and 1991, covering a contiguous region of Wisconsin and Iowa ( 1- 3). The most recent Newborn Lung Project cohort covers the entire state of Wisconsin and includes all VLBW admissions during 2003 and 2004. Reflecting a trend toward de-centralization of NICU care, there are now 16 level III NICUs in the state. This recent population-based cohort gives us the opportunity to compare VLBW infants in Wisconsin to infants born at centers that are part of a prominent national network of NICUs. National vital statistics show that the percentage of births that are VLBW has increased from 1.3 to 1.5 percent since 1990 ( 4). In the state of Wisconsin, the percentage of births that are VLBW has increased from 1.1 to 1.3 since 1995 ( 5). The Wisconsin infant mortality rate across all birthweights declined steadily until 2004, and has leveled off in recent years ( 6). Exogenous surfactant and antenatal steroid therapy to enhance lung maturity of preterm infants are thought to be responsible for much of the increased survival ( 3; 7). Well-equipped, experienced NICUs also have contributed to the increasing survival of VLBW neonates ( 8- 11). The decrease in mortality among VLBW infants was initially accompanied by an increase in early life morbidities such as intraventricular hemorrhage, bronchopulmonary dysplasia, and necrotizing enterocolitis ( 7; 12; 13). The increases in these morbidities have leveled off in recent years ( 14). Results from the first Newborn Lung Project cohort showed a decreased mortality rate and an increased incidence of bronchopulmonary dysplasia among VLBW infants from the presurfactant to postsurfactant eras ( 3). Recently published work has reported a similar increase in the incidence of bronchopulmonary dysplasia ( 15). Characteristics of NICUs, such as annual volume and the presence of a pediatric residency program, have been investigated as contributing factors to neonatal outcomes. Higher annual NICU volume has been associated with lower risk for mortality ( 10; 16) and severe IVH ( 17), while no association was found between mortality and the presence of a residency program ( 18) in the one study that investigated this relationship. We report on maternal and infant characteristics, NICU practices, and outcomes in the Newborn Lung Project, a population-based cohort of all Wisconsin VLBW infants born during the current era of neonatal care and representing all NICUs, including a range of volume, and with and without residency programs. The objectives of this paper are to (1) describe maternal and infant characteristics, NICU practices, and the incidence of neonatal morbidities in the 16 NICUs in Wisconsin; (2) explore the association between NICU-level variables and the incidence of neonatal morbidities; and (3) compare outcomes in Wisconsin to outcomes of large academic neonatal centers in the National Institute of Child Health and Human Development Neonatal Research Network. The institutional review boards of the University of Wisconsin, Madison and participating centers approved the study protocol. Study population The Newborn Lung Project Statewide Cohort is a prospective study of all VLBW infants admitted 1/1/2003 – 12/31/2004 to the 16 level III NICUs in Wisconsin ( Table 1). | Table 1Very low birthweight admissions to level III neonatal intensive care units in Wisconsin, 2003-2004 |
Data collection and variable definition Twenty-five designated trained neonatal nurses at participating centers abstracted deidentified data from each infant's medical record onto standardized forms ( 19). We collected perinatal data, including pregnancy complications, multiple pregnancy, maternal antenatal steroid therapy to enhance fetal lung maturity, tocolytic therapy to halt premature labor, and outborn status (infant transfer from place of birth to level III NICU). Infant characteristics included birthweight, gestational age, race, sex, and Apgar score for health assessment of the newborn (higher score means better newborn health). Infants who had birthweights ≤1000 grams were classified as extremely low birthweight (ELBW). The Score for Neonatal Acute Physiology II was calculated, and used as an indicator of generic baseline physiologic status in the first 12 hours of life (higher scores indicate worse health) ( 20). We also collected data on NICU care, such as surfactant therapy, fraction of inspired oxygen at 24 hours of life, ventilation treatment, intubation, postnatal steroid therapy, and length of stay in hospital. The following infant diagnoses were also recorded: intraventricular hemorrhage, bronchopulmonary dysplasia, necrotizing enterocolitis, patent ductus arteriosus, and retinopathy of prematurity. Two NICU-level structure variables were considered. The mean annual volume of infants admitted to the NICU was determined by taking the average of the 2003 and 2004 admissions ( 6). The presence of a residency program was defined as having a pediatric residency or a neonatal fellowship program at the hospital ( 21). Statistical analysis Statistical analyses were performed using SAS, version 9.1 (SAS Institute Inc., Cary, North Carolina). Means, standard deviations, frequencies, and percentages were used to describe the Newborn Lung Project cohort. We used logistic regression to examine the association between NICU-level characteristics and neonatal outcomes, while adjusting for the following case mix variables: birthweight, gestational age, sex, one-minute Apgar score, Score for Neonatal Acute Physiology II, and outborn status. During 2003 and 2004, 1463 VLBW infants were admitted to the 16 level III NICUs in Wisconsin. VLBW admissions to each NICU over this two-year time period ranged from 23 to 256. The number of infants in the Newborn Lung Project cohort was compared to the number of VLBW NICU admissions during 2003 and 2004 reported by the Wisconsin Interactive Statistics on Health ( 6). The number of births to Wisconsin residents with birthweight <1500 grams in our cohort was 1385, a close match to the 1386 births reported by WISH (one infant in our dataset had missing data for state of residence). Thus, our cohort contains all infants born during 2003 and 2004 VLBW who survived to admission to all level III NICUs in the state of Wisconsin. Maternal characteristics The mean (standard deviation, SD) maternal age was 28 (6.1) years, with 5% of mothers <18 years old. Ninety-two percent of mother received prenatal care. Pregnancy-induced hypertension was diagnosed among 28% of mothers; prolonged rupture of membranes for >24 hours was diagnosed in 17% of mothers; and 8% of mothers were diagnosed with chorioamnionitis (infection of the placenta and amniotic fluid). Antenatal steroids were administered to 69% of mothers before delivery, and 57% received tocolytics. Sixty-one percent of mothers had a caesarean section delivery ( Table 2). Maternal characteristics varied between the NICUs. For example, diagnosis of prolonged rupture of membranes ranged from 9-34% between NICUs, and diagnosis of chorioamnionitis ranged from 0-22%. There were also differences between NICUs in the percentage of mothers who received antenatal steroids (53-89%) and tocoloytic therapy (51-83%). The rate of cesarean section deliveries ranged from 54-84%. | Table 2Maternal and infant characteristics for the Newborn Lung Project Statewide Cohort Study, 2003-2004 |
Infant characteristics Twelve percent of the infants were born at hospitals without level III NICUs and were transferred to participating centers after birth (outborn status). Twenty-seven percent of VLBW infants were multiple births and 25% were small for gestational age. The mean (SD) birthweight was 1049 (298) grams and the mean (SD) gestational age was 28 (3) weeks. Several infant characteristics varied between study NICUs. The percentage of outborn infants ranged from 0-28%; the percentage of infants who were small for gestational age ranged from 15-33%; and the percentage of white infants ranged from 18-94% between NICUs. Mean birthweight ranged from 960-1192 grams and the mean the Score for Neonatal Acute Physiology II ranged from 12.9-27.1, indicating that the illness severity level of the infants varied considerably between NICUs. Table 2 shows birth and early characteristics of the VLBW cohort and the range between NICUs. Practices and outcomes in Wisconsin NICUs Table 3 shows the variation in NICU practices and outcomes between participating centers. Seventy-seven percent of infants received surfactant, ranging from 41-91% between NICUs. Overall, 76% of infants were intubated, with a range of 48-91% between NICUs. Postnatal steroids were administered to 18% of cohort infants, ranging from 4-45% between NICUs. There was a wide range in the median days on supplemental oxygen (medians ranged from 0-61 days) and the median days on ventilation (0-27 days). As expected, more ELBW infants received surfactant, were intubated, and received postnatal steroids than did VLBW infants. The group of ELBW infants also had a higher median number of days on supplemental oxygen and ventilation than the group of VLBW infants, and had a longer stay in the NICU ( Table 3). | Table 3Selected neonatal intensive care unit practices and outcomes of the Newborn Lung Project cohort by birthweight category |
Table 3 also shows variation in neonatal diagnoses between the 16 NICUs. The overall incidence of any grade intraventricular hemorrhage was 23%, with a range of 9-41% between NICUs. Grade III or higher intraventricular hemorrhage was diagnosed in 8% of the entire cohort, ranging from 0-18% between NICUs. Twenty-four percent of the VLBW cohort was diagnosed as having bronchopulmonary dysplasia, with a range of 8-56% between the 16 NICUs. The incidence of necrotizing enterocolitis ranged from 0-21%; patent ductus arteriosus incidence ranged from 21-47%, and grade III or higher ROP ranged from 0-35% between NICUs. As expected, the incidence of each of these morbidities was higher among the group of ELBW infants ( Table 3). The mean annual volume for 2003-2004 ranged from 13 VLBW admissions per year to 146 VLBW admissions per year. Three of the NICUs had a pediatric residency program or neonatal fellowship program. There was not a significant association between annual NICU volume and risk for any of the neonatal outcomes examined ( Table 4). After adjusting for case mix, infants at NICUs with a residency program tended to have a lower risk for grade III or higher intraventricular hemorrhage. Infants who were cared for at NICUs with residency programs were at higher risk for bronchopulmonary dysplasia and necrotizing enterocolitis, and showed a trend toward being more likely to die before NICU discharge ( Table 4). | Table 4Odds ratios* and 95% confidence intervals for the association between NICU structure characteristics and neonatal outcomes |
Comparison of NICU practices and outcomes in Wisconsin with national data Wisconsin infant characteristics and NICU practices were compared to those in the Neonatal Research Network for infants born between 1997 and 2002. The mean birthweight of infants in the Newborn Lung Project was similar to the mean birthweight of infants in the Neonatal Network (mean (SD), 1049 (298) and 1033 (289) grams, respectively). The percentage of infants from multiple-birth pregnancies was similar in the two cohorts, with 27% in the Newborn Lung Project and 26% in the Neonatal Network, while the percentage of infants who were small for gestational age was slightly higher in the Newborn Lung Project (25%) than in the Neonatal Network (21%). NICU practices differed somewhat between the Newborn Lung Project and the Neonatal Network. Fewer mothers of infants in the Newborn Lung Project cohort received antenatal steroids than in the Neonatal Network (69% vs 79%) and more infants in the Newborn Lung Project cohort received surfactant (77% vs 58%). There were slightly more cesarean deliveries among infants in the Newborn Lung Project than the Neonatal Network (61% vs 58%). The administration of postnatal steroids was similar across the two cohorts (18% in the Newborn Lung Project and 17% in the Neonatal Network). The incidence of major neonatal morbidities was similar among the two cohorts. The incidence of bronchopulmonary dysplasia was slightly higher among Newborn Lung Project infants than Neonatal Network infants (24% vs 22%), while the incidence of grade III or higher intraventricular hemorrhage was somewhat lower among Newborn Lung Project infants than Neonatal Network infants (8% vs 12%). The incidence of necrotizing enterocolitis was 7% in each of the cohorts. Slightly more infants in the Newborn Lung Project survived to discharge (88%) than in the Neonatal Network (85%). This report summarizes infant and maternal characteristics, survival and the incidence of major neonatal morbidities, and NICU care practices for a Wisconsin cohort of VLBW infants born over two years and receiving recent neonatal care. We also compared characteristics, survival and morbidities, and NICU care between the 16 NICUs in Wisconsin, and compared outcomes in Wisconsin to those in a cohort of infants cared for in major academic NICUs. In the first cohort of the Newborn Lung Project (1988-1991 births), we evaluated mortality and neonatal morbidities, as well as the receipt of perinatal therapies ( 3). Survival was higher and the incidence of major morbidities, such as intraventricular hemorrhage and bronchopulmonary dysplasia, was lower for infants in the more recent cohort than for those in the first cohort. Additionally, the use of both surfactant and antenatal steroids has increased. Results from the most recent Newborn Lung Project cohort show a rather wide variation in the survival rate of infants, the incidence of major neonatal morbidities, and NICU care practices between the 16 level III NICUs in Wisconsin. In order to investigate whether NICU-level characteristics help explain some of the variation between NICUs, we investigated whether annual volume and the presence of a pediatric residency program were associated with neonatal outcomes, as these have been identified as important factors in the literature. Our results suggest that while annual volume seemed to have little association with neonatal outcomes, the presence of a residency program may be associated with higher risk for bronchopulmonary dysplasia and necrotizing enterocolitis, and lower risk for at least grade III intraventricular hemorrhage and for death before NICU discharge. Results from other studies that have evaluated the effect of NICU volume have been mixed. A study of NICUs in California found that infants born at level III NICUs with low volume were at higher risk for death than infants born at level III NICUs with high volume ( 10). Annual volume was not associated with neonatal mortality among infants born during 1992-1993 at NICUs participating in the Vermont Oxford Network ( 18), but analysis of Vermont Oxford Network infants born between 1995 and 2000 found a threshold effect, such that higher volume was associated with lower mortality risk up to 50 admissions per year, and higher mortality above 50 admissions per year ( 16). Among infants in the Canadian Neonatal Network, larger NICU volume was associated with lower risk for severe intraventricular hemorrhage (grade III or higher) ( 17). To our knowledge, the relationship between NICU volume and other neonatal morbidities has not been evaluated in other studies. After adjusting for patient level characteristics, the presence of a pediatric residency program was not associated with neonatal mortality among infants in the Vermont Oxford Network ( 18). Among infants in the Newborn Lung Project, being cared for at a NICU with a residency program showed a trend toward being associated with increased mortality, and was significantly associated with higher risk for BPD and NEC, while it was associated with lower risk for grade III or higher intraventricular hemorrhage. Infants at two of the three NICUs in the Newborn Lung Project that have residency programs were doing more poorly shortly after birth than infants at the NICUs without residency programs, with higher mean values on the Score for Neonatal Acute Physiology II. Each of these NICUs also had a rather high percentage of patients that were born elsewhere and transferred in for care. It could be that the NICUs with residency programs are serving different populations of infants than NICUs without residency programs, and that our adjustment for case mix to take into account baseline illness severity was not adequate to account for these differences. It is not clear what differentiates NICUs with and without residency programs, and further investigation is warranted to determine what is contributing to the poor outcomes with respect to mortality and some of the neonatal morbidities and how outcomes may be improved. The National Institute of Child Health and Human Development Neonatal Research Network is a network of NICUs at academic research hospitals that report on neonatal outcomes for infants weighing 500-1500 grams ( 22). These centers generally represent cutting edge neonatal care in the US. Their recent report of neonatal outcomes combines data from their 1997-1998, 1999-2000, and 2001-2002 data collection periods as there was very little difference in any of their parameters across these years ( 14). Compared to the national Neonatal Research Network data, our Wisconsin cohort of VLBW infants had similar incidence rates for major neonatal morbidities, but NICU care practices were somewhat different in Wisconsin and the Neonatal Network. For example, fewer Wisconsin mothers received antenatal steroids (69%) than mothers of infants in the Neonatal Network (79%) and more Wisconsin infants received surfactant (77%) than those in the Neonatal Network (58%). While variation in outcomes and NICU practices was more substantial between NICUs in the Newborn Lung Project than the Neonatal Network, there was quite a bit of variation in outcomes and practices between NICUs in the Neonatal Network as well. Ranges in practices and outcomes reported from the Canadian NICU Network, another population-based cohort of VLBW infants, were also quite large ( 23). It is likely that the smaller amount of variation seen for Network NICUs is due to the much larger sample size for these NICUs arising from more years of follow-up. The Newborn Lung Project and Neonatal Network cohorts differ in some significant ways. First, the Newborn Lung Project is a population-based cohort that includes all VLBW admissions in Wisconsin. As the cohort includes infants born at all the level III NICUs in Wisconsin, NICUs with and without residency programs are included, and a wide range of annual admissions is represented among cohort NICUs. In contrast, each of the NICUs in the Neontatal Network is at a large research university hospital and the cohort is not population-based. The Neonatal Network evaluated outcomes for infants who weighed 500-1500 grams, while the Newborn Lung Project included all VLBW NICU admissions (≤1500 grams). However, birthweight was similar across the two cohorts, as only 40 infants (3%) had birthweight less than 500 grams in the Newborn Lung Project, and the mean (SD) birthweight in each cohort was very similar (1049 (298) grams for the Newborn Lung Project and 1033 (289) grams in the Neonatal Network). Despite the differences between the Wisconsin and national cohorts, the groups of infants in each are rather similar, as the incidence rates of most major neonatal morbidities are quite comparable. The difference in care practices between the Newborn Lung Project and the Neonatal Network could be indicative of differences in physician habits in university and non-university settings. The incidence of mortality and neonatal morbidities, in addition to NICU care practices, vary widely between NICUs in Wisconsin. Neonatal care and outcomes in Wisconsin are similar to care and outcomes reported in the National Institute of Child Health and Human Development Neonatal Research Network. These similarities indicate that Wisconsin is doing well compared to some of the leading NICUs in the US.
| Table 5Selected patient characteristics, neonatal intensive care unit practices and outcomes of Wisconsin very low birthweight infants and the National Institute of Child Health and Human Development Neonatal Research Network. |
Source of funding: 5 RO1 HL38149-17 “Risk Factors in Bronchopulmonary Dysplasia” The Newborn Lung Project involved the following investigators and project and center coordinators: - Coordinating Center, University of Wisconsin, Madison, Wisconsin: Dr. Mari Palta, Principal Investigator, Dr. Mona Sadek-Badawi, Project Director, Aggie Albanese, Kathleen Madden, Lisa Loder, and Tanya Watson;
- Dr. Christopher Green, University of Wisconsin, Madison, Wisconsin;
- Dr. David Carlton and Karin Smylie (University of Wisconsin, Madison, Meriter Hospital, Madison, Wisconsin);
- Dr. Jeffrey Garland, Roberta Einsiedel, Kathy Weaver and Jackie Sevallius (St Joseph's Regional Medical Center, Milwaukee, Wisconsin);
- Dr. Chandra Shivpuri, Susan Plachinski, and Karen Dorfler (Sinai Samaritan Medical Center, Milwaukee, Wisconsin);
- Dr. James Opitz, Sandy Freeman, MaryAnne Lach, and Angie Linneman (St. Joseph's Hospital, Marshfield, Wisconsin);
- Dr. Marie Weinstein and Laura Ziebarth (St. Mary's Hospital, Madison,Wisconsin);
- Dr. Paul Meyers, Denise Turnmeyer, and Pamela Verhagen (Children's Hospital of Fox Valley, Neenah, Wisconsin);
- Dr. Joseph Brand and Lana Reinke (St. Vincent Hospital, Green Bay, Wisconsin);
- Dr. John Wolf, Jane Friday and Joan Hintz (Columbia - St Mary's Hospital, Milwaukee, Wisconsin);
- Dr. Nancy Herrell and Sharon Nelson (Waukesha Memorial Hospital, Waukesha, Wisconsin);
- Dr P Sasidharan (Childrens Hospital of Wisconsin, Milwaukee, Wisconsin);
- Dr Gregory Milleville, Melissa Grooms and Carolyn Kraly (Aurora Women's Pavilion, West Allis, Wisconsin);
- Dr. David.Sheftel , Michelle Stampa, Monica DaPra, Sandy Anderson and Diane Fiebig (St Luke's Hospital, Racine, Wisconsin);
- Dr. Jeffrey Thompson, Shawn Dunlap (Gunderson Lutheran Hospital - La Crosse, La Crosse, Wisconsin);
- Dr. Dennis Costakos, Karen Smith and Lynn Dahlen (Franciscan Skemp Hospital, La Crosse, Wisconsin);
- Dr. Howard Kidd, Nicole Stephani and Tracy Heiman (St Elizabeth Hospital, Appleton, Wisconsin);
- Dr. Frank Mattia and Patti Davis (Aurora BayCare, Green Bay, Wisconsin);
- Dr. Lee A. Muscovitz and Deborah Peters (St Mary's Hospital, Duluth, Minnesota)
| | Bronchopulmonary dysplasia (BPD) | Chronic lung disease of prematurity. Defined as receiving supplemental oxygen at 36 weeks postmenstrual age (gestational age plus chronological age) (24;25). | | | Intraventricular hemorrhage (IVH) | A bleeding inside or around the ventricles, the spaces in the brain containing cerebral spinal fluid. Graded on a scale of I-IV, with IV being the most severe (26). | | | Necrotizing enterocolitis (NEC) | Gastrointestinal disease that mostly affects premature infants. | | | Patent ductus arteriosus (PDA) | A type of congenital heart defect in which a blood vessel that is supposed to be shut soon after birth remains open. | | | Retinopathy of prematurity (ROP) | A disease that affects immature vasculature in the eyes of premature babies. Graded on a scale of I to IV, with IV being the worst. |
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