Exposure to just three to four consecutive days of extreme heat during pregnancy may increase the risk of delivering a low-birth-weight baby, according to a national study led by researchers from the University of Queensland-IIT Delhi Academy of Research (UQIDAR), IIT Delhi and the University of Queensland.
Published in the peer-reviewed journal Environmental Research Communications, the study analysed 209,266 births recorded across India between 2015 and 2020 to examine how exposure to extreme heat at different stages of pregnancy affected birth outcomes.
The researchers found that exposure to three to four consecutive “sweltering” days during pregnancy was associated with a statistically significant increase in the risk of low birth weight. Heat exposure during the first trimester was linked to a higher risk of preterm birth, while exposure during the second trimester was associated with low birth weight.
The findings are particularly relevant for states such as Andhra Pradesh and Telangana, where prolonged summers are frequently marked by recurring periods of intense heat.
Unlike previous studies that relied on average or peak temperatures, the researchers assessed heat exposure using consecutive “sweltering” days, defined as days when the India Heat Index exceeded the 90th percentile of the local long-term climate. This approach allowed them to better capture the impact of sustained heat exposure during pregnancy.
The analysis showed that each additional consecutive sweltering day during pregnancy increased the odds of low birth weight by about one per cent after adjusting for other influencing factors.
Lead author Vineetha Vincent from UQIDAR said that although the increase associated with each additional day of heat exposure appeared modest, its cumulative impact across India’s large population could become a significant public health concern.
“While the per-day increase is small, it compounds over a long, hot pregnancy and affects a very large population, making it a meaningful public health concern in a country where extreme heat is becoming more common,” Vincent said.
The study also highlighted significant social disparities in heat-related pregnancy outcomes. Mothers with no formal education or only primary education were more likely to have a low-birth-weight baby or experience a stillbirth as heat exposure increased, compared with women who had higher levels of education.
According to Sagnik Dey, Professor at IIT Delhi and co-author of the study, climate adaptation strategies must account for these inequalities.
“The mothers most exposed to extreme heat are often those with the fewest resources to cope with it: the poorest, the least educated and the undernourished. Any adaptation response that ignores this social gradient will miss the women who need protection most,” Dey said.
The researchers said the findings highlight the need to recognise pregnant women as a priority group in India’s heat action plans, particularly as climate change contributes to more frequent and intense heat events. They added that targeted interventions, including improved access to cooling, hydration, antenatal counselling and community awareness, could help reduce heat-related risks during pregnancy.
The findings were published in the peer-reviewed journal Environmental Research Communications.
