Purpose: The objective of this study was to compare two salient neonatal outcomes-respiratory disorders and hyperbilirubinemia-between late-preterm (34-36 weeks) and full-term (37-41 weeks) singleton infants both at the population level and within families.
Methods: Analyses were based on natality data on all births in the state of New Jersey from 1996 to 2006 linked to newborn hospital discharge records. For population-level models, logistic regression analyses were conducted to estimate unadjusted and adjusted differences in outcomes by gestational age. For within-family analyses, unadjusted and adjusted logistic fixed-effects models were estimated with the latter including factors that differed across births to the same mother.
Results: Late-preterm birth increased the odds of a neonatal respiratory condition by more than fourfold (odds ratio, 4.08-4.53) and of neonatal hyperbilirubinemia by more than fivefold (odds ratio, 5.11-5.93) even when comparing births to the same mother and controlling for demographic and economic, behavioral, and obstetric factors that may have changed across pregnancies.
Conclusions: Based on population-level and within-family models, this study provides the strongest evidence to date that late-preterm birth is an important risk factor for adverse neonatal outcomes that other studies have found are associated with cognitive and behavioral disorders in childhood.
Keywords: Late preterm; Near term; Neonatal hyperbilirubinemia; Neonatal jaundice; Neonatal morbidities; Neonatal respiratory conditions; Within-family analyses.
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