And hot weather may affect a baby’s development in other ways: A 2021 analysis found a higher incidence of anomalies, such as cardiac defects, spina bifida, or cleft lip, at higher temperatures. A 2019 study took existing research that linked heat exposure to congenital heart defects and extrapolated how many such cases we can expect in the coming years: The authors estimated that over an 11-year period, an additional 7,000 babies will be born with congenital heart defects in the eight US states they studied. According to Bonell, there’s also early evidence from animals that heat stress may be triggering epigenetic changes linked to long-term adult chronic diseases such as heart disease and diabetes.
And in the United States, any potential harm to a fetus brings with it other concerns. Pregnant people, more than ever in a post-Roe world, are at risk of criminalization for behavior that may harm the fetus, particularly in states that recognize fetal personhood, which grants legal rights to a fetus from conception. “You might live in a state that criminalizes your adverse birth outcome because you took a walk when it was hot, or you were working outdoors when the temperatures were too high,” says Adelle Dora Monteblanco, an assistant professor of public health at Pacific University in Oregon.
As the research linking extreme heat to pregnancy complications piles up, public health bodies, including the World Health Organization and UNICEF, have started to take notice and include pregnant people and their unborn babies in warnings during extreme heat—although some, like the United Kingdom, are still leaving pregnant people out.
While including pregnant people in public health messaging is important, doctors also need to do more to keep patients fully informed on how to stay safe. “We know enough to act,” says DeNicola. “While we don’t have perfect solutions, we do have counseling we can give.” He knows to tell his patients to drink more water, and try to access any kind of cooling, if they have the means. If air-conditioning isn’t an option at home, people should look for cooling centers, or shopping malls, movie theaters, or libraries.
Research has shown that more targeted advice is still a necessity. A 2022 paper concluded that current guidance for pregnant people with regard to heat exposure is “sparse, inconsistent, and not evidence based.” Big questions remain, like at what stage in the pregnancy is the mother and fetus most at risk, or at what temperature conditions shift from risky to dangerous.
Yet there are limits to simply giving out advice. As the world heats up, pregnant people and their babies will continue to be vulnerable to these risks—particularly people from low-income households and people of color. Bonell points out that what people really need is practical help or the tools to help themselves. “You need some other solutions that aren’t just about education,” she says.