Relationship Between Pre-Pregnancy Body Mass Index and Gestational Age–Specific Risk of Stillbirth and Perinatal Death in Women With Chronic Hypertension

Obesity is an important risk factor for adverse birth outcomes. Its prevalence has steadily increased over the past decades, with nearly half of pregnant women in the United States considered overweight or obese in 2019. A higher pre-pregnancy body mass index (BMI) is associated with an elevated risk of stillbirth, and obesity is associated with chronic hypertension, diabetes mellitus, and other comorbidities that are independent risk factors for stillbirth and perinatal death. Because of these risks, earlier delivery for women with high BMI is being considered; however, the data on specific risks related to gestational age (GA) are limited. Currently, recommendations for women with high BMI differ across professional bodies. The Canadian Society of Obstetricians and Gynaecologists recommends delivery at 39 to 40 weeks' gestation for women with extreme obesity and at 38 to 40 weeks' gestation for those with chronic hypertension. In contrast, the American College of Obstetricians and Gynecologists and the Royal College of Obstetricians and Gynaecologists provide no GA-specific recommendations for obesity. The aim of this study was to evaluate the association between pre-pregnancy BMI and GA-specific risk of stillbirth, and whether chronic hypertension modifies these associations.This was a retrospective cohort study, using data from the National Center for Health Statistics on women who had a singleton live- or stillbirth at ≥20 weeks' gestation between 2016 and 2017. Excluded were live births and fetal deaths at