As the number of extreme heat days continues to rise due to climate change, the high temperatures are taking a toll on our health—extreme heat has been linked to a range of health issues, including heatstroke, dehydration, and respiratory problems. But some people are at greater risk than others: warmer days are putting pregnant people at a higher risk for health complications.
One Climate Central analysis published on May 14 found that extreme heat caused by climate change is posing dangerous risks for maternal health and birth outcomes. Between 2020 to 2024, the average number of pregnancy heat-risk days—defined as days in which maximum temperatures are warmer than 95% of temperatures observed in a given location—doubled in 222 countries. The greatest increase in heat-risk days occurred primarily in developing areas with limited access to health care, including the Caribbean, parts of Central and South America, and sub-Saharan Africa.
“Pregnant women and their fetuses are more vulnerable to climate-related changes, especially around heat and extreme heat,” says Shruthi Mahalingaiah, associate professor of environmental, reproductive, and women’s health at the Harvard T.H. Chan School of Public Health. Mahalingaiah adds that, when it comes to extreme heat, someone who is pregnant might not be able to regulate temperatures in the same way as someone who is not. “This is because the pregnant woman’s body is already undergoing vast changes to accommodate supporting a fetus, and it’s harder to regulate and especially cool the fetal environment to a healthy range.”
Enduring this extreme heat puts expectant mothers at a greater risk of developing high-risk conditions like pre-eclampsia and gestational diabetes, says Anna Bonell, assistant professor at the London School of Hygiene & Tropical Medicine.
It also impacts the fetuses’ development. “The fetus doesn’t have its own capacity to regulate its temperature, and we know that [much of] the development of the fetal organs are temperature sensitive,” says Mahalingaiah. Some studies have linked exposure to extreme heat with increased risk of birth defects including neural tube defects like spinal bifida.
“We also know very clearly now that you have an increased risk of pre-term birth, still birth, smaller babies, as well as congenital abnormalities [when exposed to extreme heat],” says Bonell. One 2024 study published by the journal JAMA Network Open found that the rates of preterm and early-term births increased when local temperatures were abnormally hot for more than four consecutive days. Pre-term births can have wide-reaching health impacts for a child. “A baby that’s born pre-term has an increased risk of dying, and also then has an increased risk of multiple hospitalizations and ongoing illnesses,” Bonell adds.
Extreme heat is also impacting the effectiveness of contraception and pregnancy tests—items which can be easily damaged by high temperatures, rendering them ineffective. One analysis from MSI Reproductive Choices found that, since 2011, an estimated 11.5 million women in 26 countries have had their access to contraception disrupted due to climate-related displacement.
And although climate change is impacting everyone, the health risks are greatest amongst marginalized communities. “Lower income populations [who have] less access to health care are going to be at a natural disadvantage for all things,” says Howie Wu, assistant professor of environmental health sciences at Columbia University. Individuals that don’t have access to air conditioning and shade are more susceptible to heat-related complications, while those who live close to highways are likely to face greater exposure to pollutants.
Other climate related stressors have also been linked to pregnancy complications. Air pollution has been found to increase the likelihood of high blood pressure during pregnancy, low birth weight, preterm birth, and negative impacts on fetal brain and lung development, according to the World Health Organization. And a 2020 study published in Environment International found that severe storms, like cyclones and hurricanes, could trigger early births, due to factors such as increased stress, environmental contamination, and disruption of health services.
The impact of extreme weather on accessing care can have a range of consequences. A December 2023 report published by XDI, a data driven organization that quantifies climate risks, found that human-driven climate change has increased the risk of damage to hospitals by 41%—and experts note that disruptions can have ripple effects. “In New York City, for example, Hurricane Sandy led to consequences when it came to the [ability to provide] prenatal care,” says Wu. “These extreme weather events have consequences on care providers that I think are underappreciated and probably understudied.”
Experts all stress, however, that much more work needs to be done to understand the way our changing climate is impacting pregnancies and fetal development. “It’s very important to think about the upstream and the downstream in the reproductive life cycle for pregnant people,” says Mahalingaiah. “And we have a lot more work to do to really understand it all.”
