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Study: Extreme heat increases risk for preterm delivery, stillbirth, study finds

Nov. 4 (UPI) — Exposure to high-temperature climates during pregnancy increases an expectant mother’s risk for preterm delivery and stillbirth, an analysis published Wednesday by BMJ found.

The review of data from 70 studies that included reports from 27 countries worldwide found that risk for preterm delivery rose by 5%, on average for every 1-degree Celsius — about 1.8 degrees Fahrenheit — increase in temperature and by 16% during heatwaves, the data showed.


In studies focusing on the United States in the analysis, risk for preterm delivery increased by up to 10% for every 10-degree F rise in temperature, according to the researchers.

Preterm delivery rates also were two to four times higher for Black American and Hispanic American women, the data showed.

Meanwhile, in eight included studies with data on stillbirths, the likelihood of stillbirth also increased by 5% for a 1-degree C rise in temperature, the researchers said.

Increases in global temperatures raise concerns about the effects of heat on health, especially in vulnerable groups such as the elderly, those living in poverty and the chronically ill, they said.

The findings “could have a major impact on public health as exposure to high temperatures is common and escalating” due to climate change, the researchers, from the University of the Witwatersrand in South Africa, wrote.

The study “highlights the need to identify interventions targeting heat-related conditions in pregnant women, especially in women at the age extremes and in lower socioeconomic groups, and to determine their effectiveness,” they said.

Roughly 15 million babies worldwide are born preterm each year, and it is the leading cause of death among children aged 5 years and younger, according to the World Health Organization.

In addition, nearly 2 million stillbirths occur each year globally, the WHO reports.

For this analysis, the researchers reviewed data from 70 studies.

Preterm births — babies born less than 37 weeks into pregnancy — occurred in just under 6% of the pregnancies in the included studies, lower than the global average — according to the WHO — of about 10%, according to the researchers.

Of the 47 studies that assessed preterm births, 40 reported that they were more common at higher temperatures, the researchers said.

Stillbirths occurred at a rate of 6.2 per 1,000 births in the eight included studies that addressed the issue, and all eight studies detected an increase in stillbirths at higher temperatures, they said.

The associations between temperature and stillbirth were most pronounced in the last week or month of pregnancy, according to the researchers.

Low birth weight, which is also associated with a range of short and long-term complications for newborns, occurred in 3% of the infants in the included studies, the researchers said.

Of the 28 studies that assessed birth weight, 18 found an increased risk for low birth weight babies at higher temperatures, though the effects were small, they said.

Pregnant women “merit a place alongside the groups typically considered as at high risk for heat related conditions,” the researchers wrote.

“Given increases in the frequency and intensity of heatwaves, the number of pregnant women exposed to these conditions worldwide and the … burdens associated with preterm birth and stillbirth, research and policy initiatives to deal with these connections are a high priority,” they said.

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