Background: Preeclampsia is characterized by alterations in angiogenic factors that may increase neonatal morbidity independent of preterm birth.

Methods: We estimated the controlled direct effect of preeclampsia on neonatal outcomes independent of preterm birth among 200,103 normotensive and 10,507 preeclamptic singleton pregnancies in the Consortium on Safe Labor (2002-2008). Marginal structural models with stabilized inverse probability weights accounted for potential confounders in the pathway from preeclampsia to preterm birth to neonatal outcomes, including mediator-outcome confounders related to preeclampsia status, such as cesarean delivery. Controlled direct effects of preeclampsia on perinatal mortality, small for gestational age (SGA), neonatal intensive care unit (NICU) admission, respiratory distress syndrome, transient tachypnea of the newborn, anemia, apnea, asphyxia, peri- or intraventricular hemorrhage, and cardiomyopathy were estimated for the hypothesized intervention of term delivery for all infants.

Results: When delivery was set at ≥37 weeks, preeclampsia increased the odds of perinatal mortality (odds ratio = 2.2 [95% confidence interval = 1.1-4.5], SGA = (1.9 [1.8-2.1]), NICU admission (1.9 [1.7-2.1]), respiratory distress syndrome (2.8 [2.0-3.7], transient tachypnea of the newborn (1.6 [1.3-1.9]), apnea (2.2 [1.6-3.1]), asphyxia (2.7 [1.5-4.9]), and peri- or intraventricular hemorrhage (3.2 [1.4-7.7]). No direct effect of preeclampsia at term was observed for anemia or cardiomyopathy. Our results appear robust in the presence of moderate confounding, and restriction to severe preeclampsia yielded similar findings.

Conclusion: Preeclampsia was directly associated with adverse neonatal outcomes beyond morbidity mediated by preterm birth. Although severe neonatal outcomes were less common at later gestational ages, marginal structural models suggested elevated neonatal risk due to preeclampsia even if it was possible to deliver all infants at term.