Gestational diabetes is on the rise and a Canadian study may have found out why

Gestational diabetes is on the rise worldwide, and a new Canadian study said the reason for it may not be linked to previous speculation such as obesity, maternal age or lack of exercise.

The increase could be that screening methods for gestational diabetes — a type of diabetes that occurs during the second or third trimester of pregnancy — have improved.

The study out of British Columbia and published Monday in the Canadian Medical Association Journal (CMAJ) said in Canada, the rate of gestational diabetes rose to seven per cent in 2014 from four per cent in 2004 across all racial and ethnic groups.

“We were interested in understanding why rates of gestational diabetes were increasing in British Columbia. What we found was that rates of gestational diabetes … there was a change in the way that we screen for diabetes, which has really been taken up in British Columbia,” explained Elizabeth Nethery, lead author of the study and PhD in the School of Population and Public Health at the University of British Columbia.

“We’ve been using a much more sensitive method to screen, and we found that that change in screening practice has really led to the almost doubling of gestational diabetes cases in British Columbia.”

The jump in diabetes in pregnancy has previously been linked to maternal age (the risk of diabetes when pregnant goes up with age), less exercise and poor diet, but the authors argued this is likely not the case.

The researchers looked at data from more than 550,000 pregnancies in B.C. from 2005 to 2019 as well as screening methods. During the study period, diagnoses of gestational diabetes doubled, to 14.7 per cent from 7.2 per cent in the province, and so did the amount and type of screenings.

In order for someone to be diagnosed with gestational diabetes, a glucose screening test needs to be completed.

“Fifteen to 20 years ago, screening was really considered more optional and that has changed. And now we recommend that everybody gets screened in pregnancy,” Nethery said.

Although it’s not mandatory, Diabetes Canada recommends that doctors screen all women between the 24th and 28th weeks of pregnancy.

There are two types of screenings that are used.

The first type is a one-step screening method that consists of a single two-hour glucose tolerance test. The second type is a two-step screening method, which consists of a one-hour glucose challenge test, followed by a two-hour oral glucose tolerance test for patients who screen positive.

The advantage of the one-step screening is that only one laboratory visit is needed, but this single visit takes several hours and requires fasting and three blood samples, the study said.

“The difference with this kind of one-step approach is that it actually catches quite a lot more people than the previous methods that we were using,” Nethery explained, meaning the use of this method could lead to more diagnoses of gestational diabetes.

Whether it’s a one- or two-step approach, there isn’t a universal method for gestational diabetes screening in Canada. In fact, it varies not only from province to province, but also city to city.

Dr. Jennifer Yamamoto, assistant professor of internal medicine at the University of Manitoba, said because of the lack of uniformity, the glucose test is “quite controversial.”

“We see a lot of variety, whether people do the one- or two-step approach,” she said. “For example, at my centre here in Winnipeg, most people will do the two-step approach. But we still have a number of clinicians who are ordering the one-step approach. So it’s very practitioner-dependent and very regional.”

Currently, Diabetes Canada recommends the two-step gestational screening method.

Another problem of gestational diabetes screening is the method is not typically recorded in data registries or hospital discharge summaries, the authors said, and this could explain why the increase in cases of the condition remains unknown.

Although there is a lack of data, the B.C. researchers were able to examine the one- and two-step screening information using medical insurance billing. They then examined a group of pregnancies in B.C. using glucose tolerance screenings (either the one- or two-step process) between 2004 and 2019.

Between 2005 and 2018, screening for gestational diabetes in the province went up to 95.5 per cent from 87.2 per cent. And the use of the one-step screening methods went from zero in 2005 to 39.5 per cent in 2019, the study found.

The authors found the increase was largely due to changes in gestational diabetes screening practices, from a two-step screening process to a more sensitive one-step screening process.

“We found that change in screening in particular really bumped up the proportion of people that were being diagnosed (with gestational diabetes),” Nethery said.

Gestational diabetes can lead to a number of pregnancy complications if not properly managed. High blood sugar during pregnancy can lead to preeclampsia, abnormal sugar levels in the baby and possible birth injury due to the baby’s large size, according to Diabetes Canada.

Treatment for the condition can be as simple as lifestyle changes, like diet and physical activity; however, some women need to inject insulin in order to manage it.

After delivery, the condition usually goes away, but in severe cases, some women and babies can develop Type 2 diabetes later on in life.

Because gestational diabetes can require a lot of medical involvement during pregnancy (such as more tests and ultrasounds), the more people diagnosed, the more strain on the health-care system, Yamamoto said.

“While newer randomized controlled trials have demonstrated that the one-step approach diagnosis a lot more diabetes, it doesn’t actually improve outcomes at a population level,” she argued.

The one-step screening method picks up gestational diabetes at lower sugar levels, meaning health-care providers can pick up more “mild forms” of the condition.

“And those are the types of diabetes that maybe don’t benefit from the additional treatment, as we would see in people with more severe, higher blood sugars,” Yamamoto said.

Nethery agreed.

If a person is diagnosed with gestational diabetes, there are more tests, medical visits and ultrasounds and the person is more likely to be induced, she said.

“These not only have a cost to the system, but they also have a lot of individual implications for people,” she said. “And we are potentially kind of over-diagnosing people who especially are on the lower range of blood sugar.”

— With files from Global News’ Katherine Ward