Manifest diabetes after gestational diabetes: a double-cohort, long-term follow-up in a Danish population.

Purpose: The aim was to follow-up two cohorts of women with GDM to investigate the incidence and time of diagnosis of manifest diabetes mellitus (DM) postpartum and identify the risk factors for diabetes in our population.

Methods: A follow-up study on two independent cohorts having oral glucose tolerance test (OGTT) in 1991/1992 and 2011-2016: Cohort 1 consisted of 406 women including 54 with GDM and 352 with a non-GDM OGTT-test and cohort 2 had 433 women diagnosed with GDM. The first cohort had nearly 25 years of follow-up and gave information on magnitude, conversion rate and type of diabetes manifestation. The second cohort was started recently to evaluate whether newer diagnostic criteria and baseline information on the old cohort are still valid for prediction of diabetes risk.

Results: The risk of manifest diabetes in cohort 1 at the end of follow-up was six times higher in women with previous GDM compared with non-GDM (RR = 6; 95% CI 4-11). We observed a 70% diabetes rate 25 years after pregnancy. Only family history of diabetes in cohort 2 was associated with conversion to manifest diabetes (p = 0.002), also after adjustment for age, BMI, non-Danish origin and smoking during pregnancy (p < 0.001) CONCLUSION: The incidence of diabetes after GDM is higher than that previously reported in Scandinavian populations and the rate of manifest diabetes rises steeply 15 years after pregnancy and after 40 years of age. The women of cohort 2 with recent GDM are at risk of DM at a higher rate. On this background our results are useful in identifying the time where GDM women may benefit from the effective implementation of evidence-based treatment to postpone and advert manifest DM.