Gestational Weight Gain and Adverse Pregnancy Outcomes in Women with Gestational Diabetes Mellitus and Obesity

Background/Objectives: The association between gestational weight gain (GWG) and adverse outcomes in individuals with gestational diabetes mellitus (GDM) and obesity remains unclear. This study aimed to evaluate the relationship between total GWG and maternal, obstetric, and neonatal outcomes in patients with GDM, stratified by obesity class. Methods: This retrospective cohort included 695 pregnant individuals with GDM treated at a tertiary university hospital in Brazil between 2007 and 2021. GWG was categorized as insufficient, adequate, or excessive per National Academy of Medicine guidelines. Outcomes included maternal, obstetric, and neonatal events. Analyses were conducted for the entire cohort and stratified by obesity class (I and II/III), using multivariate regression models adjusted for maternal age, parity, and pre-pregnancy BMI. Results: The mean age was 33.6 (SD 5.7) years. GWG was insufficient in 33.2%, adequate in 28.2%, and excessive in 37.8%. Excessive GWG was associated with increased odds of cesarean delivery (OR 1.69; 95% CI 1.15–2.48) and large-for-gestational-age newborns (OR 3.29; 95% CI 1.61–6.46). As a continuous variable, GWG was positively associated with cesarean delivery (OR 1.04), LGA (OR 1.10), and birthweight (β = 0.02). Lower GWG was independently associated with reduced preeclampsia risk (OR 1.09 per kg). Insufficient GWG was not linked to increased risk of small-for-gestational-age newborns or other adverse outcomes and was associated with lower insulin requirement. Results remained consistent across obesity subgroups, except for cesarean delivery in class II/III obesity. Conclusions: In individuals with GDM and obesity, insufficient GWG was not associated with increased adverse outcomes, while excessive GWG was consistently linked to unfavorable maternal and neonatal risks. Stricter GWG control may be safe and beneficial in this population.