Gestational weight gain and perinatal outcomes in pregnancies with prepregnancy bmi ≥ 50 kg/m²

Objective: To compare perinatal outcomes in pregnancies with prepregnancy BMI ≥50 kg/m² across prespecified gestational weight-gain categories, and to describe maternal characteristics more frequently observed among individuals with preterm delivery. Study Design: Retrospective cohort study of singleton pregnancies (June 2002–April 2020) at a tertiary academic institution comparing maternal and neonatal outcomes across four prespecified gestational weight-gain categories using unadjusted group-based analyses: weight loss/no gain, 0.45–4.5 kg (1–10 lb), 5.0–9.1 kg (11–20 lb), and >9.1 kg (>20 lb). Statistical comparisons used Kruskal–Wallis H, Mann–Whitney U, Welch ANOVA, and chi-square tests (α=0.05), with Holm's correction applied for multiple comparisons. Results: Of 525 identified pregnancies, 483 met inclusion criteria. Groups 1–4 included 89, 113, 93, and 188 pregnancies, respectively. The cohort was predominantly parous (73.7%) and non Hispanic Black (65.1%), with high rates of chronic hypertension (43.5%) and preexisting diabetes (10.1%). Preterm delivery occurred in 14.9% of individuals. Compared with term deliveries, those delivering preterm were older (30 vs 28 years; p=0.01), had higher prepregnancy BMI (55.4 vs 54.1 kg/m²; p=0.026), and were more likely to have chronic hypertension and preeclampsia (both p<0.01). Fetal growth restriction was more frequent in the weight loss/no-gain group (p=0.02), and infant birth weight increased linearly with greater gestational weight gain (p<0.01). No consistent trend in perinatal complications was observed across weight-change categories. Conclusion: In pregnancies with BMI ≥50 kg/m², perinatal outcomes did not differ consistently across weight-gain categories. Birth weight increased linearly with greater weight gain, while fetal growth restriction occurred more frequently with weight loss/no gain. Preterm birth was more frequent among older individuals with chronic hypertension, preeclampsia, and higher prepregnancy BMI; however, independent contributions remain undetermined from unadjusted comparisons. The relationship between gestational weight loss and fetal growth restriction warrants prospective confirmation.