Aim: To determine the frequency of major congenital anomalies in the offspring of women with gestational diabetes (GDM), classified according to their postpartum glucose tolerance status.
Methods: A prospective study of pregnancies in women with Type 1 diabetes (n = 221), Type 2 diabetes (n = 317) and GDM (n = 1822) between 1985 and 2000 (15 years). Congenital anomalies were detected by antenatal ultrasound or postnatal examination.
Results: The frequency of major congenital anomalies in the offspring was 5.9% (95% confidence interval (CI) 3.2-9.8) for women with Type 1 diabetes; 4.4% (95% CI 2.4-7.3) for women with Type 2 diabetes; and 1.4% (95% CI 0.9-2.0) for women with GDM. Two hundred and thirty-seven women with GDM (13%) had diabetes diagnosed on early (6-week) postpartum glucose tolerance testing. The frequency of major congenital anomalies in their offspring was 4.6% (95% CI 2.3-8.2), compared with 0.9% (95% CI 0.5-1.5) for the remainder of the GDM group (P < 0.0001).
Conclusions: GDM is not a homogeneous group with regard to the risk of major congenital anomalies. In those with diabetes on early postpartum testing, who are likely to have had unrecognized Type 2 diabetes antedating their pregnancy, the rate of major congenital anomalies is the same as for women with established Type 1 or Type 2 diabetes. In the remainder of the GDM group, the rate does not differ from the non-diabetic background rate.