Low-Dose Aspirin during early pregnancy May Reduce Heat-Related Risk of Preterm Birth: JAMA

A new study published in the Journal of the American Medical Association showed that starting low-dose aspirin early in pregnancy may help lessen the impact of heat exposure on preterm birth among nulliparous individuals. With heat stress becoming increasingly common, further research is needed to evaluate its broader effectiveness in pregnant populations and to confirm safety regarding perinatal mortality.

This study from a secondary analysis of the Global Network for Women’s and Children’s Health Research ASPIRIN trial, was conducted across several low- and middle-income countries. This research evaluated whether low-dose aspirin could modify the harmful effects of heat exposure during pregnancy, particularly the risk of delivering prematurely.

The study included 11,558 first-time pregnant individuals recruited between 6 and 13 weeks of gestation from communities and clinics in the Democratic Republic of Congo, Zambia, Kenya, Guatemala, Pakistan, and India. The participants were randomly assigned to receive either low-dose aspirin or a placebo during pregnancy.

This study analyzed prenatal heat exposure using site-specific daily maximum humid heat measurements, by focusing on shaded wet-bulb globe temperature that accounts for both heat and humidity. The primary outcome studied was preterm birth, defined as delivery before 37 weeks of gestation, with pregnancy dating confirmed by ultrasound scans performed at enrollment.

Among participants receiving placebo, 13.1% experienced preterm birth compared with 11.6% among those taking aspirin. Statistical modeling revealed that each 1°C increase in average daily maximum humid heat exposure across pregnancy was associated with a 5% increase in the odds of preterm birth overall.

In the placebo group, each 1°C rise in heat exposure was linked to a 7% increase in the likelihood of preterm birth. By contrast, no statistically significant increase in risk among those taking low-dose aspirin was found, which suggests the medication may help buffer the body against the physiological stress caused by high temperatures.

The analysis also identified a particularly vulnerable period approximately 17 to 19 weeks before delivery, during which exposure to temperatures above the local 75th percentile significantly increased the odds of preterm birth among placebo recipients. This vulnerability pattern was not observed in the aspirin group. Overall, the study suggest that low-dose aspirin could become part of future climate-health interventions for pregnancy.

Reference:

Meltzer, G. Y., Duttweiler, L. P., Saleem, S., Shankar, K., Mazariegos, M., Tshefu, A., Patterson, J. K., Chomba, E., Carlo, W. A., Goudar, S., Derman, R., Patel, A. B., Hibberd, P. L., Liechty, E., Essamai, F., Asturias, E., Babineau, D. C., Moore, J., Tuholske, C., … Wylie, B. J. (2026). Aspirin and preterm birth among pregnant people with increased heat exposure: Secondary analysis of a randomized clinical trial: Secondary analysis of a randomized clinical trial. JAMA Network Open, 9(5), e2611402. https://doi.org/10.1001/jamanetworkopen.2026.11402