Results
During the study period (2015-2018), there were 15,090,678 singleton births delivered between 20-44 weeks’ gestation in the US (Supplemental Figure 1 ). The prevalence rate of chronic hypertension was 1.8% (n=274,125). The distribution of socioeconomic factors in relation to chronic hypertension are shown inSupplemental Table 1 . Women with chronic hypertension were more likely to be older, African American, of higher parity, college educated, obese, and tobacco smokers, compared to normotensive women.
Perinatal mortality rates were higher among chronic hypertensive women (22.5 per 1000 births) compared to normotensive women (8.2 per 1000 births; Table 1 ). Among chronic hypertensive pregnancies, the rate of mortality was highest for stillbirth (16.1 per 1000 births), in comparison to early (4.6 per 1000 births) and late neonatal deaths (1.8 per 1000 births). Gestational age-specific risk of perinatal mortality (per 1000 births) among normotensive and chronic hypertensive pregnancies are described in Figure 1 . These rates were particularly high at early term, term, and late term gestations
The absolute risks and RR of perinatal mortality in pregnancies complicated by chronic hypertension are described in Table 2 . After adjusting for potential confounders, chronic hypertension was associated with 11.0 (95% CI 10.5, 11.5) per 1000 excess perinatal deaths over the normotensive group. The increase in risk of perinatal death in chronic hypertensive pregnancies was two-fold higher (adjusted RR 2.05, 95% CI 2.00, 2.10), compared to normotensive pregnancies.