Prevalence of impaired glucose tolerance and diabetes after gestational diabetes mellitus comparing different cut‐off criteria for abnormal glucose tolerance during pregnancy

Objective. To determine the prevalence of diabetes and impaired glucose tolerance after gestational diabetes mellitus in relation to different categories of glucose tolerance during pregnancy. Design. Prospective study. Setting. Four delivery departments and three hospitals in southern Sweden took part in recruitment and follow‐up. Population. Women undergoing a 75g oral glucose tolerance test during pregnancy delivering in 2003–2005. Methods . At first follow‐up, one to two years after delivery, 29% of eligible women with abnormal glucose tolerance during pregnancy had an oral glucose tolerance test – 160 with gestational diabetes and 309 with gestational impaired glucose tolerance – in addition to 167 control women. Cut‐off levels defining gestational diabetes and impaired glucose tolerance were two‐hour capillary blood glucose levels of 9.0 and 7.8mmol/l or plasma glucose 10.0 and 8.6mmol/l, respectively. Main outcome measures. Frequency of abnormal test results at follow‐up. Results: Diabetes was diagnosed in 11% and impaired glucose tolerance in 24% of women with gestational diabetes vs. 4 and 23% in those with gestational impaired glucose tolerance, respectively. Combining women with abnormal test results during pregnancy revealed diabetes or impaired glucose tolerance in 29% as compared to 10% among controls; the odds ratio (95% confidence interval) for having abnormal test results was 3.3 (1.8–5.9) in a multivariate logistic regression analysis. Conclusions: Lowering the cut‐off level for gestational diabetes to include the category of impaired glucose tolerance would identify a high percentage of women with diabetes and impaired glucose tolerance postpartum, who constitute target groups for intervention and/or diabetes prevention.