Heat linked to fewer male births in Africa and India for different reasons
Feb 23rd 2026
A study of nearly five million births finds high temperatures during pregnancy reduce male births in sub-Saharan Africa through early pregnancy loss and in India by disrupting access to sex-selective abortion services.
- Researchers analysed nearly 5 million births from 104 Demographic and Health Surveys paired with daily temperature records and published the results in PNAS on February 19, 2026.
- In sub-Saharan Africa, higher temperatures in the first trimester were associated with fewer male births, consistent with heat-triggered miscarriages affecting male fetuses more.
- A one standard deviation rise in extreme heat days above 30°C shifted the African sex ratio from about 103.5 to 101 boys per 100 girls.
- The African effect was strongest among rural women, those with little or no formal education, and mothers on their fourth child or later.
- In India, the temperature effect appeared in the second trimester and is consistent with heat disrupting access to sex-selective abortion rather than a biological effect, with an overall shift from about 110 to 109 boys per 100 girls per one standard deviation increase in 25–30°C days and larger reductions for older, high-parity, and sonless mothers in northern states.
- The authors argue climate change is unlikely to push sex ratios much further because the effect starts above 20°C, a threshold most of sub-Saharan Africa and India already exceed for much of the year.