Short spells of extreme heat during pregnancy linked to higher newborn health risks, study finds

A study of more than 209,000 births across India found that heat exposure in early pregnancy increased the risk of preterm birth, while second trimester heat was associated with low birth weight.

Even three to four consecutive days of extreme heat during pregnancy can increase the likelihood of babies being born with low birth weight, according to a nationwide study that examined more than 209,000 births across India.
The findings are particularly relevant for Andhra Pradesh and Telangana, where repeated periods of intense summer heat are common. Researchers found that short spells of extreme heat, rather than only prolonged heatwaves, were associated with poorer birth outcomes.

The study, titled Effect of extreme heat stress on adverse pregnancy outcomes in India, analysed 209,266 births recorded between 2015 and 2020. Researchers matched each birth with local heat conditions experienced throughout pregnancy, measuring exposure through consecutive “sweltering” days based on the India Heat Index rather than average temperatures.
Published in the peer reviewed journal Environmental Research Communications, the study found that each additional consecutive sweltering day during pregnancy increased the odds of low birth weight by about one per cent after accounting for other influencing factors. Low birth weight was defined as less than 2,500 grams at birth.

Researchers also found that the stage of pregnancy during which heat exposure occurred influenced birth outcomes. Extreme heat during the first trimester was associated with a higher risk of preterm birth, while exposure during the second trimester was linked to low birth weight.
The research was led by the University of Queensland–IIT Delhi Academy of Research (UQIDAR) in collaboration with IIT Delhi, the University of Queensland’s School of Public Health, the University of New South Wales, the University of Exeter and Korea University.

“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,” said Vineetha Vincent, lead author of the study from UQIDAR.
The study also found that women with no formal schooling or only primary education faced a greater risk of low birth weight and stillbirth as heat exposure increased compared with women who had higher levels of education.

“The mothers most exposed to extreme heat are often those with the fewest resources to cope with it: the poorest, the least educated, the under nourished. Any adaptation response that ignores this social gradient will miss the women who need protection most,” said Professor Sagnik Dey, co author of the study from IIT Delhi.
The researchers said the findings point to the need for heat action plans to identify pregnant women as a priority group, particularly in regions experiencing repeated periods of extreme heat.

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