Introduction
Chronic hypertension complicates 1-5% of pregnancies, but there has been 13-fold increase in the prevalence of chronic hypertension in the United States (US) in the last four decades (1). The American obesity epidemic (2, 3), and deferred childbearing leading to older age of pregnant people,(4, 5) contribute substantially to this trend (6). Chronic hypertension during pregnancy is associated with increased rates of maternal complications, including death (7), superimposed preeclampsia (8, 9), placental abruption (10-12), end-stage renal disease (13), and long-term cardiovascular and cerebrovascular disease (12, 14, 15). Chronic hypertension is also an independent risk factor for an array of perinatal complications, including stillbirth,(16-18) fetal growth restriction,(19) neonatal death,(20, 21) as well as neurological and neurodevelopmental deficits in children.(22-24) In light of the increasing prevalence rates of chronic hypertension and the associated complications, there is a need to evaluate the impact of chronic hypertension on perinatal mortality in the US, including stillbirth and neonatal death.
Chronic hypertension is associated with increased risk of preterm delivery,(8) and gestational age at delivery impacts neonatal outcomes in pregnancies complicated by chronic hypertension.(25) Gestational age also influences obstetrical care including interventions to improve neonatal outcomes (i.e., the administration of antenatal corticosteroids to promote fetal lung maturity) as well as delivery timing.(26) In the pathway between chronic hypertension and perinatal outcomes, preterm delivery features as an important component in the causal pathway, but how and, to what extent, preterm delivery plays a role in shaping these associations remain unknown.
We undertook a population-based cross-sectional study in a large contemporary US cohort to quantify the association between chronic hypertension and perinatal mortality and to disentangle the impact of preterm delivery as mediator. We hypothesized that chronic hypertension is associated with perinatal mortality and that preterm delivery plays an important role that mediates this causal association.