Abstract
Objective : To estimate the association between chronic
hypertension and perinatal mortality and evaluate the extent to which
this risk is impacted by preterm delivery.
Design: Cross-sectional analysis.
Setting: US, 2015-2018.
Population: Singleton births from 20-44 weeks’ gestation.
Main outcomes and measures : We derived the risk of perinatal
mortality in relation to chronic hypertension from fitting log-linear
Poisson models with robust variance. Risk ratios (RR) and 95%
confidence intervals (CI) were estimated after adjusting for
confounders. The impact of misclassifications and unmeasured confounding
biases were assessed. Causal mediation analysis was performed to
quantify the impact of preterm delivery on the association.
Results: Of the 15,090,678 singleton births, perinatal
mortality was 22.5 per 1000 births in chronic hypertensive pregnancies
compared to 8.2 per 1000 births in normotensive pregnancies (adjusted RR
2.05, 95% CI 2.00, 2.10). Corrections for exposure misclassification
and unmeasured confounding biases substantially increased the risk
estimate. Although, causal mediation analysis revealed that most of the
effect of chronic hypertension on perinatal mortality was mediated
through preterm delivery, the perinatal mortality rates were highest at
early term, term, and late term gestations, suggesting that a planned
early term delivery at 37-386/7 weeks may optimally
balance risk in these pregnancies. Additionally, 87% (95% CI 84, 90)
of perinatal deaths could be eliminated if preterm deliveries, as a
result of chronic hypertension were prevented.
Conclusions: Chronic hypertensive pregnancies are associated
with increased risk for perinatal mortality. Planned early term delivery
and targeting modifiable risk factors for chronic hypertension may
reduce perinatal mortality rates.