The study, conducted by researchers from the University of Toronto, Mount Sinai Hospital and the Institute for Clinical and Evaluative Sciences, examined 21,823 women diagnosed with gestational diabetes and examined follow up records up to 9 years.
They found that the rate of diabetes increased rapidly in the first 9 months after delivery, peaking at 9 years.
"In this large, population-based study, we found that diabetes developed within 9 years after the index pregnancy in 18.9 percent of women with previous gestational diabetes; this rate was much higher than the rate among women without gestational diabetes," Dr. Denice Feig and co-authors said.
They also noted that the rate of gestational diabetes in Ontario, the study province, seems to be increasing and is linked to older mothers.
Living in low-income neighbourhoods and in urban areas were also risk factors for gestational diabetes.
Dr. Feig and colleagues postulate that higher urban statistics 'may reflect the large numbers of South and East Asian and black populations living in urban areas that have a higher risk of type 2 diabetes'.
"The main strength of our study lies in the fact that it was a large population-based study involving more than 21,000 women with gestational diabetes, with up to 9 years of follow-up," the researchers said.
"Unlike other studies, it covered a large, well-defined geographic region with a population of 13 million, which allowed us to make a more robust assessment of the risk of type 2 diabetes after gestational diabetes than has been possible in previous studies," they added.
However, the study could not 'assess the effect of ethnicity, obesity and level of fasting glucose during pregnancy, risk factors that are clearly associated with the development of diabetes.'
"These women may benefit from both preventative interventions and regular screening," researchers said.
They also pointed out that physicians and policy makers need to counsel and screen these women accordingly.
The study is published in CMAJ.