Pregnancy-induced hypertension and infant mortality: roles of birthweight centiles and gestational age

Objective To assess the effect of pregnancy-induced hypertension (PIH) on infant mortality in different birthweight centiles (small for gestational age [SGA], appropriate for gestational age [AGA], and large for gestational age [LGA]) and gestational ages (early preterm, late preterm, and full term). Design Retrospective cohort study. Setting Linked birth and infant death data set of USA between 1995 and 2000. Population A total of 17 464 560 eligible liveborn singleton births delivered after 20th gestational week. Methods Multivariate logistic regression models were applied to evaluate the association between PIH and infant mortality, with adjustment of potential confounders stratified by birthweight centiles and gestational age. Main outcome measure Infant death (0-364 days) and its three components: early neonatal death (0-6 days), late neonatal death (7-27 days), and postneonatal death (28-364 days). Results PIH was associated with decreased risks of infant mortality, early neonatal mortality, and late neonatal mortality in both preterm and term SGA births, and PIH was associated with lower postneonatal mortality in preterm SGA births. PIH was associated with decreased risks of infant mortality, early neonatal mortality, late neonatal mortality and postneonatal mortality in preterm AGA births. Decreased risk of infant mortality and early neonatal mortality was associated with PIH in early preterm LGA births. Conclusions The association between PIH and infant mortality varies depending on different birthweight centiles, gestational age, and age at death. PIH is associated with a decreased risk of infant mortality in SGA births, preterm AGA births, and early preterm LGA births.