General obstetrics: Pregnancy‐induced hypertension is associated with lower infant mortality in preterm singletons

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Abstract
Objective To assess the association between pregnancy‐induced hypertension (PIH) and infant mortality. Design Retrospective cohort study. Setting Birth and infant death registration dataset of the USA. Population A total of 17 432 987 eligible, liveborn singleton births in 1995–2000. Methods Multivariate logistic regression was applied to evaluate the association between PIH and infant mortality, with adjustment of potential confounders. Main outcome measures 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 There was a significant reduction in infant mortality associated with PIH in early preterm infants (OR = 0.59, 95% CI: 0.56–0.63) and in late preterm infants (OR = 0.80, 95% CI: 0.73–0.87), but a significant increase in term infants (OR = 1.08, 95% CI: 1.02–1.14). Both in early preterm and late preterm births, early neonatal mortality (OR = 0.38, 95% CI: 0.34–0.42; OR = 0.68, 95% CI: 0.61–0.77) and late neonatal mortality (OR = 0.59, 95% CI: 0.50–0.70; OR = 0.76, 95% CI: 0.61–0.96) were decreased in infants born to mothers with PIH compared with those born to mothers with normal blood pressure. The PIH‐associated reduction in neonatal mortality among preterm singletons was stronger in small‐for‐gestational‐age infants than in normal growth infants and stronger in infants born to nulliparous women than in those born to multiparous women. Conclusions PIH is associated with lower risk of infant death in preterm births but higher risk in term births.