(Reuters Health) - More babies could be born with heart defects in the future as global warming puts pregnant women at greater risk of exposure to dangerously high temperatures, new research suggests.

FILE PHOTO: Children cool off in fountains as a summer heatwave with high temperatures continues in Paris, France, August 3, 2018. REUTERS/Regis Duvignau

The study is preliminary, and the potential impact of climate change on congenital heart disease is far from clear, the researchers say. But earlier work has suggested that expectant mothers who are exposed to extreme heat in the spring or summer, particularly in early pregnancy, are more likely to deliver babies with heart defects.

“Early pregnancy, particularly 3-8 weeks after conception, is the critical period for a fetus’ heart development,” study coauthors Dr. Shao Lin and Dr. Wangjian Zhang, of the University at Albany in Rensselaer, New York, said in an email.

At present, congenital heart defects affect about 40,000 births per year. Their study, published in the Journal of the American Heart Association, suggests there may be as many as 7,000 additional cases over an 11 year-period.

For the study, Lin and Zhang and their colleagues estimated the number of babies expected to be born between 2025 and 2035. Then, using climate change forecasts from NASA and the Goddard Institute for Space Studies, they calculated the anticipated average rise in pregnant women’s heat exposure across different regions in the U.S. as a result of global warming.

While the authors expected to find that heat exposure in the summer would be a problem, the study also showed that “early” heat waves or extreme heat in spring could be dangerous in some parts of the country.

Pregnant women in the Midwest were most likely to be affected, followed by women in the South and Northeast regions of the country, the study suggests.

Dr. Dianne Atkins, Professor of Pediatrics at the University of Iowa in Iowa City, cautions that the data from the study is preliminary and is based only on estimates.

“We cannot be certain” that heat exposure will increase the risk of congenital heart disease, “but it would be prudent for women to avoid becoming overheated during the early weeks of pregnancy,” Atkins, who was not involved in the study, told Reuters Health by email.

The authors of the study agree, advising that pregnant women try to reduce outdoor activities and stay cool during extremely hot weather.

Dr. Geoffrey L. Rosenthal, Co-Director of the Children’s Heart Program at the University of Maryland Children’s Hospital, told Reuters Health by email that the study’s findings “can be used to develop risk mitigation strategies that are specific to particular geographic regions and seasons, and allow for more efficient allocation of public health resources.”

“The analysis is robust and thoughtful,” he added. “Whether the predictions deriving from the analysis will be observed will depend on the validity of the models used to generate the input for these predictions.”

A distinct advantage of this report, he said, is that it is the first time, to his knowledge, that such predictive modeling has been applied “to a rare but impactful health outcome, congenital heart defects.”

SOURCE: bit.ly/2BL1acy Journal of the American Heart Association, online January 30, 2019.