Introduction
Gestational diabetes mellitus (GDM) is the most common medical problem in pregnancy and a common risk associate for subsequent development of type 2 diabetes (T2DM). Very high rates are reported and cited from international studies which are at variance with clinical experience in Australia1. This study examines the rate of T2DM with up to a 25 year follow up.
Methods
The data used for this study were obtained from women in an ethnically representative population, diagnosed with one criteria and managed by one practitioner. The women were seen with a diagnosis of GDM over a 20 year period, 1991 to 2010. Women contacted were asked whether they had developed diabetes and if not, would they be agreeable to have a HbA1c test. If not known, diabetes was diagnosed if the HbA1c was ≥ 6.5%. If women declined a HbA1C test their self-report of no diabetes was recorded.
Results
From this 20 year period there were 3,266 women referred with GDM of whom 2,510 could be considered for this study and 1,305 (51.9%) could be contacted. Of these women, 729 (55.9%) declared their diabetes status. Diabetes status was determined through self-report or HbA1c testing. 69 women reported that they were diagnosed as having diabetes and an additional 3 were diagnosed with T2DM through HbA1c testing. For women who were diagnosed with GDM in 1991-1995, 1996-2000, 2001-2005 and 2006-2010 respectively, the proportion who developed diabetes between diagnosis of GDM and 2016 was 18.9%,16.7%, 10.6% and 2.3%. The overall proportion of women who developed diabetes during the 25 year follow-up period was 9.9%.
Conclusion
The incidence of T2DM after a pregnancy complicated by GDM ranges from 2.3% 5-10 years after completion to 18.9% 20-25 years later. These figures are far lower than what is frequently cited in the international literature.