It is known that temperature during pregnancy can have an effect on the number of male vs female babies born (the sex-ratio) among animals. An interesting study suggests that this is also true for humans.
The study found that exposure to days with a temperature 20 degrees Celsius (68 degrees Fahrenheit) or higher during the nine months of pregnancy leads to fewer male births. While at first glance that doesn't seem so warm, these areas also had days 30 degrees Celsius (86 degrees Fahrenheit) and higher.
The study was done by linking data on 5 million live births in 33 sub-Saharan countries and India with temperature data. The researchers observed fewer male births after high first-trimester temperature exposure. This was consistent with increased spontaneous abortions due to mother's heat stress. This is especially true for mothers in rural areas, with little education. (No air conditioning!)
From Euronews: As temperatures rise, the number of male births is decreasing, study finds
When temperatures rise above 20°C, fewer baby boys are born compared to girls, a new study has found.
Researchers at the University of Oxford found that heat exposure can increase prenatal mortality in early pregnancy, particularly among males.
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