Context: In diabetic pregnancy, neonatal hypoglycemia (NH) is usually attributed to insufficient regulation of maternal glycemic control. Recent data suggest that maternal body mass index (BMI) could have an influence. Objective: Our objective was to determine whether an association exists between maternal prepregnancy BMI category and occurrence of NH among infants born to women with gestational diabetes mellitus (GDM). Design and Setting: This was a retrospective study including all GDM pregnancies delivered between 1986 and 2006 at a tertiary care center (Hospital de la Santa Creu i Sant Pau, Barcelona). Patients and Outcomes: GDM was diagnosed using universal screening and National Diabetes Data Group criteria. Two thousand ninety-two newborns (1925 singletons, 85% of total GDM offspring) were studied. NH was defined according to Cornblath criteria. In addition to maternal BMI, we considered other variables such as glucose values at diagnosis or third-trimester glycated hemoglobin as potential predictors of NH. We explored whether the association between maternal BMI and NH could be due to intermediate steps such as cesarean section or abnormal birth weight. Results: The rate of NH was 3%. In the bivariate analysis, prepregnancy BMI was higher in the NH group (24.45 vs. 23.19 kg/m2, P < 0.02). In the logistic regression analysis, prepregnancy BMI of at least 25 kg/m2 was independently associated with NH whetherthe analysis included intermediate variables (odds ratio = 2.11; 95% confidence interval = 1.10-4.03) or not (odds ratio = 2.66; 95% confidence interval = 1.44-4.92). Conclusions: Pregestational BMI should be considered among the predictors of NH in offspring of women with GDM. Copyright © 2012 by The Endocrine Society.