Although most pregnant women with gestational diabetes return to a euglycemic state after delivery, they are generally considered at increased risk of developing overt type 2 disease later in life. Published estimates of the incidence of diabetes mellitus in such women vary widely, between 3% and 70%, and the true risk is unknown.
Through the use of a population-based database, the authors identified all deliveries in the province of Ontario over a 7-year period (1995 to 2002) and linked these data with another database to identify mothers previously diagnosed with gestational diabetes. They followed these women for 9 years after delivery.
Over the 7-year study period, 659,164 pregnant women without preexisting diabetes were identified; of these 21,823 (3.3%) had a diagnosis of gestational diabetes. The incidence of gestational diabetes in Ontario over the 9-year study period increased from 3.2% in 1995 to 3.6% in 2001 (P < .001); diabetes developed in 3.7% of women by 9 months and 18.9% by 9 years.
Multivariable analysis showed that a history of gestational diabetes during the index pregnancy was the most significant factor associated with the risk of developing diabetes after delivery (hazard ratio 37.28, 95% CI 34.00–40.88; P < .01). Other factors associated with an increased risk of type 2 diabetes after the index delivery included higher age, lower income, urban residence, no prior pregnancy, development of hypertension, and higher number of increased primary care visits before delivery. Diabetes developed at a higher rate in women with gestational diabetes delivering in the most recent study period (1999–2001) than in those with an earlier delivery (1995–1996); 16% of women who delivered in the most recent study period developed diabetes within 4.7 years, while it took 9.0 years for those in the earlier delivery period to reach 16%.
The risk of overt type 2 diabetes among women with a history of gestational diabetes found in this large population-based study suggests to the authors that targeted regular screening and preventive interventions may be beneficial.