Pre-gestational maternal body mass index predicts an increased risk of congenital malformations in infants of mothers with gestational diabetes


Dr M. L. Martínez-Frías, Directora del CIAC, Instituto de Salud Carlos III, Sinesio Delgado 6 (Pabellón 6), 28029, Madrid, Spain. E-mail:


Aims  The aim of the present study was to identify characteristics in women diagnosed with gestational diabetes mellitus (GDM) that could be predictive of congenital malformations in their infants.

Methods  Using data from the Spanish Collaborative Study of Congenital Malformations (ECEMC), a hospital-based case-control study and surveillance system, we assessed the relationship between a number of maternal variables, including pre-gestational body mass index (BMI), and specific congenital malformations in their infants.

Results  The overall risk for a selected group of congenital malformations in an infant of an obese mother with GDM compared with an obese mother with normal glucose tolerance (NGT) was 2.78 (1.38–5.55, P < 0.001). Within the group of mothers with GDM, obesity (BMI ≥ 30 kg/m2) was associated with a significantly increased risk of cardiovascular defects compared with non-obese women [OR = 2.82 (1.31–7.04), P < 0.01]. In mothers with NGT, pre-gestational BMI was not associated with congenital malformations.

Conclusion  Pre-gestational obesity is a predictive variable for congenital malformations in infants of mothers with GDM. The greater their BMI, the higher the risk for congenital malformations in their offspring. Given the blastogenic origin of the congenital defects identified, and the relationship between obesity and Type 2 diabetes, it is probable that this increased risk is as a result of previously unidentified pre-gestational diabetes mellitus (PGD). It is important that overweight and obese women planning a pregnancy be evaluated for the presence of diabetes.