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.