Confounders
We adjusted for several confounders including maternal age
(<15, 15-19, 20-24, 25-29 [reference], 30-34, 35-39, and
≥40 years), education (below high school, up to high school, college,
and beyond college educated), race/ethnicity (non-Hispanic White,
non-Hispanic Black, Hispanic, or other race), maternal smoking
(non-smoker [reference], smoked before pregnancy only, and smoked
before and during pregnancy), single marital status, pre-pregnancy
body-mass index (BMI in kg/m2; underweight
[<18.5], normal [18.5-24.9], overweight
[25.0-29.9], obese [30.0-34.9], and morbidly obese [≥35.0]),
and pregestational diabetes. We also adjusted for year of delivery to
address potential temporal changes in the prevalence of chronic
hypertension and maternal mortality.