Association between body-mass-index and gestational-age-specific rates of stillbirth in women with and without chronic hypertension

Body-mass-index (BMI) specific recommendations to inform optimal timing of delivery are scarce. This study describes gestational age-specific risks stillbirth in women with varying pre-pregnancy BMI and assesses how these change the presence chronic hypertension (CH). was a retrospective cohort all singleton births United States, 2016-2017. Rates per 1000 total were compared by between categories, stratified CH. Piecewise additive mixed models used estimate association possible effect modification Models adjusted for relevant factor (e.g., age, smoking etc). These also compare age using fetuses-at-risk approach. The included 7,363,952 birth; 254,225 (3.5%) underweight, 3,220,432 (43.9%) had normal BMI, 1,918,480 (26.1%) overweight 1,062,177 (14.4%), 516,693 (7.0%), 365,357 (5.0%) class I, II III obesity, respectively. increased from 3.85 8.26 obesity III. Women without CH 14.2 4.7 stillbirths births, Average joint effects led 3 5 times rates who normotensive hazard ratio 4.68, 95% CI 3.73 - 5.86). increases varied across (p < 0.001), sharper at late term post-term gestation, especially hypertension. Overweight obese risk stillbirth, this is compounded concurrent Gestational differences suggesting an early gestation accompanied