Rising heat and humidity driven by climate change may be influencing pregnancy outcomes and conception patterns in Nigeria, according to a study led by researchers at the University of Michigan. The research, published in the Proceedings of the National Academy of Sciences, examined the relationship between humid heat and pregnancy in Nigeria, a country with one of the world's highest fertility rates and significant vulnerability to climate change.
Researchers noted that humidity had received limited attention in studies of climate change and reproductive health, particularly in low- and middle-income countries. High humidity makes it harder for the body to cool itself, increasing the risk of heat stress. The team analysed two rounds of the Nigeria Demographic and Health Surveys, covering pregnancy information from 2003 to 2016. They combined the data with satellite observations and weather station records to estimate exposure to humid heat across the country.
Using daily maximum wet-bulb globe temperatures between 1983 and 2016, the researchers assessed the combined effects of temperature and humidity. Study co-author Cascade Tuholske, now a professor at Aix-Marseille University in France, said combining satellite and ground-based data could improve heat exposure estimates in countries such as Nigeria, where long-term weather records are limited.
The findings showed that greater exposure to humid heat was strongly associated with an increased likelihood of early pregnancy terminations. However, the surveys did not establish whether these were induced or spontaneous. Nina Brooks, an assistant professor at the University of Michigan's School for Environment and Sustainability, said both could potentially be affected, although physiological, spontaneous pregnancy loss was considered a more plausible explanation.
The study also found that exposure to high levels of humid heat over a month was associated with a 1.4 per cent decline in conceptions, compared with an average of slightly more than 15 conceptions per 1,000 woman-months. Conceptions subsequently rose by 2.3 per cent above the average in the following month and by five per cent after two months. The researchers said the overall probability of conception increased, but the timing of pregnancies shifted.
Study co-author Katie McMahon, a doctoral candidate at the University of California, Santa Barbara, said the changes might reflect how people adjust to heat exposure. However, shifts in pregnancy timing could create social and economic pressures for households, especially when they conflict with women's childbearing preferences.
The effects were more pronounced among women with less education and those living in rural areas. Geographical differences were also evident, with shifts in pregnancy timing more marked in northern Nigeria, while the south showed less impact or a different pattern.
Kwaw Andam, a co-author and former Nigeria country programme leader for the International Food Policy Research Institute, said the regional differences reflected longstanding development disparities that social policies had yet to address adequately.
The researchers said understanding how humid heat affects pregnancy across different communities could help public health officials provide better guidance to women. Brooks called for more research linking large-scale findings with the lived experiences of women and communities, noting that understanding how people perceive heat-related health risks could help shape more effective public health advice.