Chronic Hypertension, Perinatal Mortality, and the Impact of Preterm
Delivery: A Population-Based Study in the United States, 2015-2018
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.