Background
Women with gestational diabetes mellitus (GDM) are likely to develop diabetes in later life. International reports and reviews indicate a variable but generally high rate of conversion. However, data from international reports are difficult to apply to an Australian population.

Aim
To investigate in Australia, in a representative population, the prevalence of diabetes developing in women who have been diagnosed with one criteria and who have had uniform standards of clinical care.

Material and methods
This study considered women referred with a diagnosis of GDM according to the Australasian Diabetes in Pregnancy Society criteria and seen by one practitioner over a 20 year period, from 1991 to 2010. The area of referral had an ethnic distribution similar to the overall Australian demography.

Results
Despite, in some cases, being more than 25 years since the pregnancy, more than half the women were contactable and the majority agreed to have their diabetes status declared or determined. The overall prevalence was 10.3%. The prevalence at each 10 year age increment was more than twice the figure reported from the AusDiab study. A higher maternal body mass index and a positive family history of diabetes were the strongest predictive factors. The prevalence of undiagnosed diabetes was 0.9%.

Conclusion
In a representative population, after GDM, the prevalence of diabetes of 10.3% was far lower than that reported internationally but was still about twice the rate for the overall Australian population.