Gestational Weight Gain and Perinatal Outcomes in Pregnancies with Prepregnancy BMI = 50 kg/m²

To compare perinatal outcomes in pregnancies with prepregnancy body mass index (BMI) ≥ 50 kg/m² across prespecified gestational weight-gain categories, and to describe maternal characteristics more frequently observed among individuals with preterm delivery.

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 to 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.

Of 525 identified pregnancies, 483 met inclusion criteria. Groups 1 to 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 years 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 (FGR) 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.

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 FGR 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 FGR warrants prospective confirmation.

· In pregnancies with BMI ≥ 50 kg/m2, outcomes did not differ consistently by weight gain categories.. · Birth weight increased linearly with greater weight gain.. · FGR occurred more frequently with weight loss/no gain.. · Prematurity was more frequent with older age, hypertension, preeclampsia and higher prepregnancy BMI..