Objectives Long term follow up women with gestational diabetes mellitus (GDM).

Design Case–control study.

Setting Academic obesity unit.

Population Women earlier identified as having gestational diabetes mellitus.

Method Twenty-eight women diagnosed with GDM in 1984–1985, and a control group (n= 52) who gave birth at the same time performed a 2-h oral glucose tolerance test 15 years later. Basic anthropometry and questions about various aspects of eating and exercise habits were furthermore obtained.

Results Ten women (35%) in the GDM group were diagnosed with type 2 diabetes mellitus and none in the control group (P < 0.001). Mean BMI in the diabetic group was 27.4 kg/m2 and in the non-diabetic GDM group 24.6 kg/m2 (P < 0.05). The mean weight gain since the first child was 8.4 kg in all GDM versus 8.1 kg in controls (ns). The women who developed type 2 diabetes mellitus, however, gained 15.1 kg since the birth of their first child (P < 0.05).

Conclusions Women who are diagnosed with GDM have a considerably higher risk of developing type 2 diabetes mellitus later in life. Despite a close medical monitoring during pregnancy, the further follow up within the health care system and information about long term consequences of GDM for later type 2 diabetes mellitus development seems to be generally lacking. More active strategies for future weight control and lifestyle advice after delivery might therefore be indicated for women with GDM.