A study published Thursday in the journal Diabetes Care found rates of both gestational and pre-gestational diabetes among Ontario women doubled between 1996 and 2010.
The magnitude of the jump in incidence over the 14-year period came as somewhat of a surprise, said lead researcher Dr. Denice Feig, an endocrinologist at Mount Sinai Hospital who heads the Toronto hospital's Diabetes in Pregnancy Program.
"I have a clinic of women with gestational diabetes (GDM) and pre-gestational diabetes and we've certainly been noticing a marked increase in numbers in our clinics, so I expected that there would be a rise," she said.
"But I suppose I didn't expect there to be a full doubling in both the GDMs and pre-GDMs, so that was a surprise."
To conduct the study, researchers examined administrative health data for more than 1.1 million Ontario women who went through pregnancy from 1996 to 2010.
About 45,000 of the women were diagnosed with gestational diabetes, which develops when placental hormones diminish the ability of insulin produced in the pancreas to properly regulate blood-sugar levels. More than 13,000 had Type 1 or 2 diabetes prior to getting pregnant, hence the term pre-gestational.
"By 2010, almost one in every 10 pregnant women over the age of 30 had diabetes in pregnancy," said Feig. "That's enormous. And most of our women are getting pregnant over the age of 30."
The rate was even higher — 13 per cent — among women over 40.
"I believe the rate of gestational diabetes is rising probably because of the mere reason that the rate of diabetes in the general population is rising," said Feig. "And the reason for that is probably increased obesity, increased fat intake in diets, poor lifestyle and decreased exercise.
"All those things put together are increasing the rates of diabetes in our population and we're seeing it in women who are entering pregnancy because these are the same risk factors for gestational diabetes."
Feig said not only is the incidence of the disease growing among Canadians in general, but doctors are increasingly seeing younger people with Type 2 diabetes, which occurs when the body either resists the effects of insulin or doesn't produce adequate amounts to maintain normal blood-sugar levels.
Researchers found that although congenital anomaly rates declined over the study period by 20 to 23 per cent in the children of women with GDM and pre-GDM respectively, the risk remained significantly elevated compared to those without diabetes.
In 2010, compared to children of non-diabetic mothers, infants born to women with pre-GDM had a two-fold higher risk of congenital anomalies, while those with GDM had a 26 per cent higher risk.
Congenital abnormalities include neural tube defects such as spina bifida and malformations of the heart, kidneys and central nervous system, all of which can lead to significant disability in children.
"Women with Type 1 and 2, we know that if you have high blood sugars around the time of conception and the first trimester, then your risks of increased congenital anomalies are high," said Feig.
"What we try to do is counsel women to make sure their sugars are very close to normal prior to conception and in the first trimester. And if women can plan their pregnancies with regards to their glycemic control, then their rates of congenital anomalies are very close to normal."
The study, which also involved researchers affiliated with the Institute for Clinical Evaluative Sciences, also found the rate of perinatal mortality — the death of fetuses after 20 weeks' gestation or of infants within 28 days of birth — remained unchanged.
However, the risk of perinatal death is higher in women with gestational or pre-gestational diabetes compared to women without the disease.
Feig said it was hoped that with the push for better blood-sugar control among women with diabetes and improved obstetric care over the 14-year period that researchers would see a reduction in perinatal mortality, "but we did not."
Women need to be encouraged to enter pregnancy at a healthy weight and not to gain too many extra pounds during pregnancy because excess weight gain is a risk factor for gestational diabetes, she said.
"So a healthy lifestyle prior to and during pregnancy may decrease our gestational diabetes rates, and women should be screened for Type 2 diabetes who have a history of gestational diabetes," she said.
"I think it's a wake-up call to physicians and people who take care of women with diabetes that the rates are getting very high and these women need a lot of support."
Feig said more needs to be done to reduce adverse outcomes related to diabetes, including pre-conception planning, improved glucose control during pregnancy and enrolling women in high-risk obstetrical care.
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