Extreme heat driven by climate change is becoming a more frequent and dangerous threat to pregnant women and their babies everywhere around the world, especially in countries without widespread access to cooling or adequate health care, finds a new report.

Between 2020 and 2024, climate change doubled the number of days hot enough to seriously harm a pregnant mother and her fetus, finds analysis from Climate Central.

These “pregnancy heat-risk days” are defined as days when the high temperature exceeds 95% of what’s historically normal for a given location. On such days, pregnant women face a higher risk of complications like gestational diabetes, preeclampsia, sepsis, and postpartum hemorrhage. Their fetuses are more likely to be stillborn or born prematurely, with preterm birth often leading to long-term health problems.

The study found that every one of the 247 countries and territories analyzed experienced at least five more pregnancy heat-risk days per year over the past five years due to human-caused climate change.

Ninety percent of the countries analyzed, and 63% of cities, saw the average annual number of pregnancy-heat risk days “at least double” from what would have been expected without climate change. Within these groupings, 32% of the countries and 18% of the cities fared even worse, experiencing “at least one additional month’s worth of pregnancy heat-risk days on average each year.”

The report finds that residents of the Caribbean, Central and South America, the Pacific Islands and Southeast Asia, and sub-Saharan Africa have been most severely exposed to extreme heat over the past five years. In nearly every case, these countries “are among the most vulnerable to the consequences of climate change despite contributing least to greenhouse gas emissions.”  

They also tend to lack broad access to both efficient cooling and health care—two supports that could help reduce the impacts of extreme heat on expectant mothers and their babies.

The Caribbean was particularly hard-hit by extreme heat during the period of study, with climate change causing many of its island nations to experience “an average of at least 60 additional pregnancy heat-risk days annually.” 

“That accounts for at least one-fifth of the duration of an average pregnancy,” Climate Central notes.

To calculate their findings, Climate Central researchers first counted the number of pregnancy heat-risk days in each location, then used the Climate Shift Index—a modeling tool—to estimate how many of those days would have occurred in a world without human-caused climate change.