In this remarkable piece of science reporting, Sarah Neville of the FT reports on an alarming new mystery that scientists have stumbled upon, namely, the strong (and rising) correlation between warmer temperatures and higher risk of pre-term (or premature) births. She calls this “a scientific mystery that some experts believe is turning, almost unnoticed, into a global public health emergency.”
Ms Neville then helps us understand the mystery more clearly: “More than 200 studies have provided compelling evidence of a link between rising temperatures and adverse pregnancy outcomes, including premature birth, stillbirth, low birth weight, congenital abnormalities and hypertensive disorders in mothers, with the earliest dating back to 1939 but a marked uptick in the past decade.
An analysis of 198 of those studies, across 66 mostly high-income countries, published in Nature last year, found that for every 1C increase in heat exposure, there was a 4 per cent increase in the odds of a preterm birth. During heatwaves, the odds increased by 26 per cent.”
So, why is this a mystery? Why can’t scientists figure out what is going on? Ms Neville writes: “…scientists are still uncertain about the biological processes through which heat causes these damaging effects. Nor is it clear how women can best protect themselves.”
Then Ms Neville tells us about what the current state of knowledge regarding this peculiar medical mystery:
“…according to many of the analyses, the association between heat and poor pregnancy outcomes is as strong in temperate countries as those that endure constant debilitating heat
….extreme heat was a relative, not an absolute concept: the danger lay in a woman’s exposure to levels of heat to which she was not acclimatised…
Ana Bonell, assistant professor at the London School of Hygiene and Tropical Medicine…has extensively studied the physiological effects of heat on pregnant women in Gambia, led an international study that in 2023 found a heightened risk of stillbirth at temperatures as low as 12C, and as high as 46C. “We see from the epidemiological evidence that actually everyone is affected,” she says. “You’re not safe anywhere.”
Women may be especially vulnerable at points in the year when temperatures rise most sharply, says Matthew Chersich, executive director at South Africa’s Wits Planetary Health Research Division and a co-author on the Nature study led by his colleague, research clinician Darshnika Lakhoo. “Spring is a particularly dangerous season for that reason,” he adds….
…the evidence suggests brief episodes of extreme heat are “particularly problematic””
Then Ms Neville helps us understand that the public health emergency risk is not limited to pre-term birth; it could be much broader than that i.e. the impact of higher temperatures during pregnancy could be on a range of health outcomes for children:
““If you’re exposed to extreme heat in utero and you survive, what happens to your health when you’re 20, 30 or 50?”
An investigation under way in South Africa, following 200 women from the second trimester to a year after birth, seeks to build on data that suggests children born during periods of extreme heat have a higher rate of admission to hospital for infections
Dehydrated mothers can also struggle to produce breast milk, leading to nutritional shortages that can affect neurodevelopment, says Renate Strehlau, the clinician scientist leading the work.”…
Veronique Filippi, a professor at the London School of Hygiene and Tropical Medicine who studies the impact of extreme heat on maternal and newborn health in Africa, says several analyses suggest heat exposure during the first trimester increases the chances of hypertensive disorders later in the pregnancy”
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