• Pregnant woman standing in front of water, tree in background, during Autumn.

    Pregnant women exposed to colder temperatures during pregnancy have a lower rate of gestational diabetes compared to those exposed to hotter temperatures, according to new Canadian Medical Association Journal research. 

Hot weather may put pregnant women at risk of developing gestational diabetes, according to new research published in the Canadian Medical Association Journal.

The study, released May 15, looked at twelve years’ worth of administrative health data of pregnant women who gave birth between 2002 to 2014 in the Greater Toronto Area.

“It’s exciting. This is the first time that temperature has been looked at in comparison to the risk of developing gestational diabetes,” says Dr. Gillian Booth, lead author of the study and a researcher at St. Michael's Hospital and the Institute for Clinical Evaluative Sciences.

Booth and colleagues used historical weather data from Environment Canada to calculate the average air temperatures study subjects were exposed to in the 30 days prior to reaching 27 weeks of pregnancy, which is when most women are screened for gestational diabetes, and cross-referenced the data with the Ontario Diabetes Database, which tracks gestational cases.

“We were blown away by the findings and the clear association between gestational diabetes and temperature,” says Booth.

Among women exposed to cold temperatures, equal to -10 degrees C or lower, nearly five per cent were registered as having gestational diabetes. That number jumped to 7.7 per cent when women were exposed to average temperatures above 24 C.

Even when adjustments were made for variables such as ethnicity, age, number of pregnancies, and socioeconomic status, Booth says the results showed the same pattern: lower temperatures were associated with lower risk, and higher temperatures associated with higher risk.

Consequences for public health with global temperatures rising

Current climate change models predict that the earth’s average surface temperature will rise by one to two per cent each year by 2050. Booth believes this could lead to an increase in the prevalence of gestational diabetes, which increases the risk of stillbirth and can result in long-term complications for both mother and fetus.

“The warming of the earth by one or two degrees might not seem like a lot but there are 15 million world-wide incidents of gestational diabetes, so it might be quite impactful,” says Booth. “And it may be more impactful with more days with extreme heat as well.”

Even small changes could be significant; the study reported a six to nine per cent increase in a woman's risk of developing gestational diabetes with every 10-degree C increase in the average temperature.

And the consequences could impact the prevalence of pre-gestational diabetes too.

“Gestational diabetes is a bit of a litmus test of who is at risk of developing Type 2 diabetes,” says Booth. “What happens with gestational diabetes is likely to also be true for diabetes in general. So, this could forecast all of them, not just the cases of gestational diabetes.”

What can Canadians do

To lower their risk of developing gestational diabetes, Booth recommends pregnant women find ways to keep cool. In hot weather, this might mean using air conditioning, seeking shade and taking care not to overdress. In winter, that could mean simply getting outside and embracing the cold. 

“Having a healthy diet and being active can already reduce your risk; this is just one thing that can be added on top to improve the likelihood of a healthy pregnancy," says Booth. 

The study was funded by the St. Michael’s Hospital Foundation and the Canadian Institutes of Health Research.