Yet another reason to worry about global warming may be an increase in the number of women who develop gestational diabetes, suggests a new study that found seasonal higher temperatures are tied to an increased risk for gestational diabetes.

Researchers found Canadian women were more likely to be diagnosed with gestational diabetes if they were exposed to higher average outdoor temperatures during pregnancy, compared to women who were pregnant in cooler periods.

"It’s compelling evidence that air temperature is tied with increasing gestational diabetes risk," said lead author Dr. Gillian Booth, of St. Michael’s Hospital and the Institute for Clinical Evaluative Sciences in Toronto.

The researchers analyzed data from 396,828 women and their 555,911 deliveries in the Greater Toronto Area from 2002 to 2014.

They compared the risk of developing gestational diabetes among women exposed to an average outdoor temperature of at most –10 degrees Celsius (C), or 14 degrees Fahrenheit (F), during the 30 days before their gestational diabetes test to women exposed to at least 24 degrees C, about 75 degrees F, before their tests. The prevalence of gestational diabetes among women exposed to colder outdoor temperatures was 4.6%, compared to 7.7% among women exposed to warmer temperatures.

Every 10 degree C increase in average outdoor temperature was tied to a 6% increase in the risk of women developing gestational diabetes, the researchers report in CMAJ online May 15.

When they restricted the analyses to women who had more than one birth during the study period, the results were similar.

The increased risk may be important as global temperatures are expected to rise 1 to 2 degrees C by 2050, Booth told Reuters Health.

"That may seem like a small number, but 10 to 15 million women around the world have gestational diabetes annually and that may potentially have a big impact," she said.

The new study can't prove that warmer temperatures cause women to have gestational diabetes, said Dr. Kathryn Drennan, a maternal fetal medicine physician at the University of Rochester Medical Center in New York.

For example, there may be other seasonal factors influencing the risk of gestational diabetes like fluctuating vitamin D levels, said Drennan, who wasn't involved with the new study.

"I think for the average pregnant women, they shouldn’t be concerned about this," she told Reuters Health. "I think from a systems–wide level, it’s a bigger concern especially with the warming climate."

The study gives researchers a reason to investigate the relationship between temperature and gestational diabetes, said Drennan.

"This is the first study I’ve seen looking at this particular aspect of gestational diabetes," she said. "It’s a nice way to start looking at this relationship."

—Andrew M. Seamn