OBJECTIVE We wished to test the hypothesis that the diagnosis of diabetes in women with previous gestational diabetes in our follow-up program had altered the ratio of IDDM to NIDDM in our pregnant population.

RESEARCH DESIGN AND METHODS We identified all pregnancies managed at the Mercy Hospital for Women in Melbourne, Australia, from 1971 to 1994 that were complicated by prepregnancy diabetes. In these 374 pregnancies, we identified those women who had previously been diagnosed with gestational diabetes mellitus (GDM). The changing prevalences over time of prepregnancy IDDM and NIDDM, as well as the contribution to both of these conditions made by women who had previously had GDM, were calculated.

RESULTS Over the period of the study, there was an increase in the prevalence of IDDM from 0.15 to 0.44% (χ² for trend, P < 0.00001) and NIDDM from 0.03 to 0.11% (χ² for trend, P = 0.0001). The proportion of all women with diabetes with NIDDM did not change significantly (16.7–20%). There was a progressive increase in the proportion of women with NIDDM who had had GDM (from 8.3 to 39.1%), but the trend was not statistically significant (P = 0.059). Women with NIDDM were more likely (20 of 64, 31.3%) to have had gestational diabetes in the past than women with IDDM (12 of 310, 3.9%, odds ratio 11.3, 95% CI 5.16–24.7, P < 0.0001).

CONCLUSIONS Despite finding relatively young women to have NIDDM, our GDM follow-up clinic has not yet altered significantly the ratio of IDDM to NIDDM in pregnancy.