Rising temperature may shift sex ratios at birth, analysis of five million births finds

Medical Xpress

February 23, 2026

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Rising temperatures during pregnancy may alter the sex ratio at birth, according to a groundbreaking study published in *Proceedings of the National Academy of Sciences*. Analyzing data from over five million births across 34 sub-Saharan African countries and India, researchers found that higher temperatures are linked to an increase in male births. This discovery has significant implications for understanding population health and gender balance in a warming world. The study, led by researchers at the University of Oxford, combined large-scale survey data with high-resolution temperature records to examine how heat exposure during pregnancy affects birth outcomes. The findings revealed that regions experiencing hotter temperatures saw a noticeable shift toward male-dominated sex ratios at birth. This suggests that environmental factors, particularly rising global temperatures, could play a critical role in shaping human demographics. While the exact biological mechanisms behind this phenomenon remain under investigation, researchers speculate that heat stress may influence hormone production or other physiological processes during pregnancy, favoring the survival of male fetuses. Such shifts in sex ratios could have far-reaching consequences for societal structures, including family dynamics and workforce composition. For public health officials and policymakers, these findings underscore the urgent need to address the broader impacts of climate change on human health. Understanding how environmental factors shape birth outcomes is crucial for preparing communities to adapt to a rapidly changing world. This research highlights the interconnectedness of climate science and human demographics, offering valuable insights into the challenges posed by global warming. Ultimately, the study serves as a call to action for further research into the long-term effects of temperature fluctuations on reproduction and population health. As temperatures continue to rise, even small shifts

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Originally published on Medical Xpress on 2/23/2026