TORONTO — Women with gestational diabetes have a one in five chance of developing Type 2 diabetes in the decade after giving birth, say researchers, who recommend regular, ongoing screening for the disease following pregnancy.

In a study of more than 21,000 Ontario women diagnosed with pregnancy-related diabetes, researchers found that almost 20 per cent had gone on to develop Type 2 diabetes within nine years of giving birth.

The rate of transition to Type 2 diabetes increased rapidly in the first nine months after delivery and peaked at nine years, said principal investigator Dr. Denice Feig, an endocrinologist at Mount Sinai Hospital in Toronto.

"About four per cent of women were found to have Type 2 diabetes within the first nine months and after that the rate was continually stable over the nine years," Feig said Monday. "It continued to climb all those years after."

"Probably the first nine months reflects women who had undiagnosed Type 2 diabetes. They probably had diabetes before the pregnancy and were not diagnosed."

Details of the 1995-2002 study, which used health records that included the Ontario Diabetes Database, are published in this week's issue of the Canadian Medical Association Journal.

The researchers also found a difference between the speed at which Type 2 diabetes developed in women from the earlier period of the study, compared to those looked at towards the close of the study.
 

The women developed diabetes at a faster rate in the later years, said Feig, explaining that among women registered in 1995-96, it took nine years for their Type 2 diabetes rate to reach 16 per cent, while for those registered in the 1999-2001 period, it took just 4.7 years to hit 16 per cent.

Dr. Stewart Harris of the University of Western Ontario, who holds the Canadian Diabetes Association chair for diabetes management, said the difference in rates likely reflects the rising tide of obesity in the Canadian population.

"We're getting fatter," Harris, who was not involved in the study, said from London, Ont.

"So if you were pregnant in 1995 and had gestational diabetes, your risk for developing (Type 2) diabetes was slower than if you were pregnant in 2005 and had gestational diabetes. Likely - and they can't prove this from the data they have - likely it's because the population is heavier 10 years later."

He said obesity - weight gain both going into and during pregnancy - is among the biggest contributors to gestational diabetes.

Feig said that age may also be a factor that raises risk, as many women have their first child later in their reproductive years, along with lower socioeconomic status and living in urban areas.

So what is it about gestational diabetes that sets some women on a path towards becoming Type 2 diabetics?

"Pregnancy is a bit of a stress test," said Feig. "You need more insulin to overcome insulin resistance during pregnancy. And if you have a genetic tendency towards diabetes, it kind of comes out in pregnancy because you can't overcome the insulin resistance and your blood sugar goes up a little bit."

"Afterward, that stress of the placental hormones goes away, but it kind of tells us you're at risk, and clearly those women are at risk because they tend to develop it later on (at a) much higher (rate) than the general population."

Feig said previous studies have shown that children born to mothers with pregnancy-related diabetes have an elevated risk for obesity and diabetes later in life.