Confounders
The choice of confounders were guided by directed acyclic graph (DAG)
(Figure 1 ). These included 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), maternal race/ethnicity (non-Hispanic White, non-Hispanic
Black, Hispanic, or other race), maternal smoking (non-smoker
[reference], smoked before pregnancy only, initiated smoking during
pregnancy, or smoked before and during pregnancy), single marital
status, and pre-pregnancy body-mass index (BMI). BMI
(kg/m2) was categorized as underweight
(<18.5), normal (18.5-24.9), overweight (25.0-29.9), obese
(30.0-34.9), and morbidly obese (≥35.0). Other confounders included
chronic hypertension, pregestational diabetes, and year of delivery.