Cohort composition
The study population included all women who delivered singleton births
in the US between 20-44 weeks’ gestation from 2015-2018. We excluded
pregnancies with multiple gestations, and records with missing
gestational age or gestational age <20 weeks and ≥45 weeks, as
well as pregnancies with missing chronic hypertension status. After all
the exclusions, 15,090,678 singleton births were included in the study
(Supplemental Figure 1 ).