Prepregnancy Obesity Versus Excessive Gestational Weight Gain: A Comparative Evaluation of Adverse Outcomes

Background/Objectives: Obesity and excessive gestational weight gain (EGWG) are known risk factors for adverse outcomes in pregnancy, but the comparative risk is less well defined and increasingly relevant in an era of increasing use of weight loss medications. We aimed to determine whether EGWG was associated with adverse maternal and neonatal outcomes, compared with prepregnancy obesity. Methods: Multicenter retrospective cohort study of pregnant patients who delivered a singleton within a single university health system from 2019-2024. Patients with missing prepregnancy body mass index (BMI) data, BMI < 18.5 kg/m², or pregestational diabetes were excluded. Logistic regression with propensity score weights and g-computation were used to evaluate if the incidence of several adverse maternal and neonatal outcomes were impacted by prepregnancy obesity and gestational weight gain (GWG). p values were adjusted for multiple comparisons. Results: Among the 129,615 pregnancies included, 28,516 (22.0%) had prepregnancy obesity, 36,943 (28.5%) were overweight prior to pregnancy, and 64,156 (49.5%) had a normal BMI prior to pregnancy. When compared to patients with obesity, patients with normal prepregnancy BMI and EGWG had a lower risk of adverse maternal and neonatal outcomes, including gestational diabetes, gestational hypertension, preeclampsia, eclampsia, cesarean delivery, and postpartum hemorrhage, as well as large and small for gestational age birthweight, stillbirth, neonatal intensive care unit admission, neonatal mechanical ventilation, respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, and sepsis. Beneficial effects were attenuated for patients with overweight prepregnancy BMI or for larger EGWG. Conclusions: Lower prepregnancy BMI, even with the potential unintended consequence of EGWG, may be more favorable than untreated prepregnancy obesity with regard to perinatal outcomes.