When temperatures rise, so do the risks for pregnant people in some of the world’s most vulnerable regions—yet a simple, low-cost intervention may offer unexpected protection. In a study led by Harvard Medical School researchers at Beth Israel Deaconess Medical Center, low-dose aspirin taken early in pregnancy appeared to shield against heat-related preterm birth, a growing threat as climate change intensifies. With an estimated 12 to 15 million babies born prematurely each year, even small increases in risk due to rising temperatures could ripple across global health systems. Now, science is pointing to a potential buffer: a 100-milligram tablet already used to prevent preeclampsia.
The findings, published May 6 in JAMA Network Open, analyzed data from over 11,500 first-time pregnant participants across seven countries in Africa, South Asia, and Latin America—all part of the Global Network for Women's and Children's Health Research ASPIRIN trial. Researchers linked each woman’s location to high-resolution climate data, measuring humid heat exposure using a composite index that accounts for temperature, humidity, sunlight, and wind. Their focus: how this real-feel heat impacted preterm birth, defined as delivery before 37 weeks.
Among those not taking aspirin, every 1°C increase in average daily humid heat during pregnancy was tied to a 5% higher odds of preterm birth—a significant rise on a population level. But for those who started daily low-dose aspirin early in pregnancy, that link vanished. The protective effect suggests aspirin may help stabilize placental function under heat stress, though the biological mechanisms remain under study.
Still, the results come with caution. While aspirin appeared to neutralize heat-related preterm birth risk, researchers observed a troubling signal: among aspirin users, heat exposure was associated with higher perinatal mortality, including stillbirth or death within one week of birth. The finding was not seen in the original ASPIRIN trial analysis and may reflect statistical noise due to low event numbers, particularly in malaria-endemic areas. Still, it underscores the need for deeper investigation before broad recommendations can be made.
"The increasing global prevalence of heat stress warrants testing the effects of aspirin more broadly among pregnant people, as well as its safety with respect to perinatal mortality," said senior author Blair Wylie, HMS professor of obstetrics, gynecology, and reproductive biology. As extreme heat becomes more frequent—with the 10 warmest years on record all within the past decade—the search for scalable, low-cost protections has never been more urgent. For now, low-dose aspirin stands as a promising, if still cautiously viewed, ally in the fight to safeguard maternal and newborn health in a warming world.