A new study from the University of Oxford indicates that when temperatures exceed 20°C, fewer baby boys are born compared to girls. Researchers found that heat exposure can elevate prenatal mortality in early pregnancy, with males being particularly susceptible.
Analyzing data from over five million births across 33 sub-Saharan countries and India, the study published in Proceedings of the National Academy of Sciences suggests extreme heat plays a role in worldwide birth ratios. "We show that temperature fundamentally shapes human reproduction by influencing who is born and who is not born," stated co-author Abdel Ghany. The findings highlight measurable consequences for fetal survival and family planning, with implications for population composition and gender balance.
The research identified 20°C as a critical threshold, although hotter days do not proportionally intensify the effect. Previous studies have noted that gestational heat exposure threatens maternal thermoregulation, increasing the risk of pregnancy loss due to insufficient blood, oxygen, or nutrients for the fetus.
Beyond biological impacts, heat exposure also influences family planning behavior. High temperatures can affect abortion access and financial stability, disproportionately impacting women with fewer resources. As global temperatures are projected to rise, researchers urge further studies on environmental factors to protect maternal health and improve healthcare access, thereby mitigating long-term effects on reproduction and population dynamics.