Women exposed to high temperatures and heatwaves during pregnancy are more likely to have premature or stillborn babies, researchers said.
Such outcomes – closely linked to poverty, especially in the tropics – will likely increase with global warming, especially during more frequent and intense heatwaves, they reported in The BMJ, a medical journal.
Even small increases “could have a major impact on public health as exposure to high temperatures is common and escalating,” the study concluded.
Each year, 15 million babies are born premature, the leading cause of death among children under five, according to the World Health Organisation (WHO).
That mortality is concentrated in the developing world, especially Africa.
To quantify the impact of higher heat on pregnancy outcomes, an international team of researchers led by Matthew Chersich from Wits Reproductive Health and HIV Institute in Johannesburg looked at 70 peer-reviewed studies of 27 rich, poor and middle-income nations.
Of the 47 studies that concerned preterm births, 40 reported they were more common at higher temperatures.
The odds of a preterm birth rose, on average, by five per cent per one degree Celsius increase, and by 16 per cent during heatwave days, according to the new findings.
Global warming has seen Earth’s average temperature rise by 1C over the last century, with greater increases over large land masses.