Background: The aim of this study was to evaluate the role of maternal body mass index (BMI) on the development of gestational diabetes (GDM) and the risk of adverse pregnancy outcomes in women who are overweight or obese. 

Methods: A prospective cohort study nested within the LIMIT randomized control trial. Women were recruited between 10⁺⁰ and 20⁺⁰ weeks’ gestation, with a BMI >25kg/m², and were categorized as either overweight (BMI 25.0-29.9kg/m²) or obese subclass 1 (BMI 30.0-34.9kg/m²), obese subclass 2 (BMI 35.0-39.9kg/m²), and obese subclass 3 (BMI > 40.0kg/m²), utilizing World Health Organization criteria. Women underwent a fasting oral glucose tolerance test at 26–28 weeks’ gestation, and a diagnosis of GDM was made if the results of fasting blood glucose were ≥ 5.5 mmol/L or blood glucose ≥ 7.8 mmol/L after two hours. Maternal antenatal and postpartum complications, and neonatal outcomes were evaluated.

Results: A total of 1,010 women formed the cohort for this analysis, with 434 (42.97%) categorized as overweight, 295(29.21%) obese subclass 1, 167 (16.53%) obese subclass 2, and 114 (11.29%) obese subclass 3. The incidence of GDM increased with increasing maternal BMI (6.91% overweight vs 12.54% obese subclass 1 vs 10.78% obese subclass 2 vs 19.30% obese subclass 3). The effects of maternal BMI and gestational diabetes on risk of clinical outcomes were independent.

Conclusion: Increasing maternal BMI is a significant independent risk factor for the development of gestational diabetes. Our findings demonstrate a considerably higher prevalence of GDM than has been previously described in women who are overweight and obese. This has significant public health implications given that GDM is a major contributor to adverse pregnancy outcome, and has long term consequences for both women and their infants.