Oxford research links heat exposure during pregnancy to decline in male births

New research by the University of Oxford has found that exposure to high temperatures during pregnancy is linked to a decline in male births.

This is according to a report released on February 23, 2026, by researchers at the university’s Department of Sociology.

The report disclosed that this adds to growing findings that extreme heat driven by climate change can influence population patterns.

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**What the report said **

According to the study, titled Temperature and sex ratios at birth, ” published in the Proceedings of the National Academy of Sciences, higher temperatures can alter the sex ratio at birth, with implications for population health and gender balance.

• _“The results show that temperatures above 20°C are consistently associated with fewer male births in both regions – but through different mechanisms. _
• _In sub-Saharan Africa, exposure to high temperatures during the first trimester of pregnancy is linked to a decline in male births. This pattern is consistent with increased prenatal mortality driven by maternal heat stress, and is particularly pronounced among women living in rural areas, those with lower levels of education, and those with higher birth orders. _
• _However, in India, where sex ratios have historically been distorted by son preference and sex-selective abortion, the effects appear later in pregnancy. Higher temperatures during the second trimester are associated with fewer male births, especially among older mothers, high-parity births, and women without sons in northern states.” _

Researchers suggest this may reflect reduced access to, or use of, sex-selective abortion, temporarily narrowing gender imbalances

**More insights **

Dr Jasmin Abdel Ghany, lead author of the Oxford study, said extreme heat is not only a major public health threat but also a force that shapes human reproduction by influencing who is born and who is not.

• _“Extreme heat is not only a major public health threat. We show that temperature fundamentally shapes human reproduction by influencing who is born and who is not born,” she said, adding that the findings have implications for foetal survival, family planning behaviour and long-term gender balance. _
• The study also found that heat exposure does not affect all populations equally. Women in vulnerable settings and those with fewer resources face greater risks, raising concerns about widening health inequalities as climate change intensifies.
• The report stressed that protecting maternal health and improving access to healthcare will be critical to reducing long-term reproductive and population impacts in a warming climate.

**What you should know **

A study projects that the number of people living with extreme heat could nearly double by 2050 if global temperatures rise, with countries like the Central African Republic, Nigeria, South Sudan, Laos, and Brazil predicted to see the most significant increases in dangerously hot temperatures, while the largest affected populations will be in India, Nigeria, Indonesia, Bangladesh, Pakistan, and the Philippines.

The research says that heat risk has already risen sharply, with about 23% of the global population living with extreme heat as of 2010, and that share is expected to grow to 41% in the coming decades.

Dr. Jesus Lizana, Associate Professor in Engineering Science at Oxford University, says most changes in cooling and heating demand will occur before global temperatures reach 1.5 °C, requiring early adaptation measures such as installing air conditioning, but temperatures will continue to rise if warming hits 2.0 °C.

He said that achieving net-zero carbon emissions by 2050 will require decarbonizing buildings and implementing resilient climate strategies.

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