Can heatwaves affect whether you have a boy or girl? Study explains

As the world becomes increasingly hotter with rising global temperatures, scientists are beginning to look into how extreme heat might impact pregnancy in ways that are not immediately obvious. In some instances, this might even extend to determining whether a baby is born male or female.One recent international study, entitled “Temperature and Sex Ratio at Birth,” has begun to indicate a potential correlation between increased temperatures during pregnancy and a slight reduction in the number of baby boys born. While the sex of a baby is predetermined at conception, environmental conditions during pregnancy do play a role in determining survival rates.What the research indicatesThis recent study looked at birth rates from India and 33 countries in Sub-Saharan Africa over a period of more than two decades. By combining this data with detailed temperature information, the researchers attempted to identify whether increased temperatures during pregnancy might impact the overall ratio of baby sexes born. In general, this ratio tends to be around 103 to 107 baby boys for every 100 baby girls.The results revealed that “warmer temperatures were associated with fewer male births overall.” In Sub-Saharan Africa, temperatures over 30°C in early pregnancy resulted in a “noticeable reduction in male births.” In India, the reduction was “smaller but still present.”The timing of exposure to high temperatures also played a role. In Africa, the impact was more pronounced in the first trimester. In India, the impact was more visible in the second trimester.A mixture of biology and societyThe researchers also believe that the differences in results may not be solely due to biological differences. In the case of India, “sociological factors have been present in the country for a long time. Son preference and sex-selective practices have been present in India for a long time.”“Sub-Saharan Africa is a setting where son preference is not known to cause sex ratio distortions, whereas in India sex-selective abortions have distorted sex ratios,” said Dr. Jasmin Abdel Ghany.This contrast enabled scientists to compare the region with the least social bias to one where social influences were known to exist, thus aiding them in their understanding of the effects of heat exposure.The research also indicates that extreme temperatures may have an indirect effect on the availability of health care. For instance, extreme temperatures may impair one’s ability to move around, which may, in turn, influence reproductive choices.Understanding the biological perspectiveFrom a biological point of view, scientists cite the “frail male” hypothesis. The hypothesis asserts that male babies are more vulnerable during conception than female babies.“The chromosomes are determined at fertilisation of the egg,” said Dr. Abdel Ghany, emphasizing that the temperature cannot change the sex of the baby. However, the environment, especially extreme temperatures, may influence the success of the conception.Exposure to high temperatures in the initial stages in these regions has shown to increase the chances of miscarriages of male foetuses. This is in line with the general belief that male foetuses demand more resources and energy during development compared to female foetuses.“We observe an effect of heat exposure in Sub-Saharan Africa in the first trimester that indicates temperature may affect survival during pregnancy with disproportionate effects for boys.”How the study was conductedThe research is based on the data of around five million births recorded in the Demographic and Health Survey. Each of the births has been linked to the temperature conditions based on the location and the estimated period of pregnancy.“We used data on 5 million births from the Demographic and Health Survey and linked each birth with high-resolution temperature conditions during pregnancy,” said Dr Jasmin Abdel Ghany.“Our regression models are seasonality-adjusted and account for differences in geographic areas,” she told South First. The overall findings of this study, when considered together, reveal a complex relationship between climate change, human biology, and human social behaviours. While further detailed data is needed, this study raises new areas of concern related to how climate change may be affecting pregnancy outcomes quietly in the future.