Early Pregnancy Body Roundness Index and Development of Adverse Pregnancy Outcomes: A Secondary Analysis of the nuMoM2b Study

Objective This study assessed the association between early pregnancy body roundness index (BRI) and adverse pregnancy outcomes in nulliparas. Methods In this secondary analysis of a multicenter prospective cohort study, waist circumference, height, and weight were measured between 6 and 13 6/7 weeks' gestation and used to calculate BMI and BRI (364.2–365.5 × {1 − [(waist circumference/2π)/(0.5 × height)] 2 } 0.5 ). Four BRI and BMI quantiles (Q1‐Q4) were defined, and rates of adverse pregnancy outcomes were compared using multivariable logistic regression. Results Among 9671 individuals, greater BRI was associated with gestational diabetes (GDM), hypertensive disorders, preterm birth, cesarean delivery, and large‐for‐gestational age infants. Discordant BRI and BMI assignments affected GDM and cesarean odds. Those with Q2 BMI but Q3–Q4 BRI had increased odds of GDM (aOR 2.28, 1.49–3.47) and cesarean (aOR 1.39, 1.15–1.68). Those with Q3 BMI and Q1–Q2 BRI demonstrated reduced odds for GDM (aOR 0.31, 0.15–0.63) and cesarean (aOR 0.75, 0.60–0.94). Participants with Q4 BMI and Q1–Q3 BRI experienced decreased odds for cesarean (aOR 0.55, 0.43–0.70) but similar GDM odds. Conclusions Greater first trimester BRI, a reflection of central adiposity, is associated with adverse pregnancy outcomes. Early pregnancy BRI may improve risk stratification for GDM and cesarean delivery beyond BMI.