Heatwaves are linked to increased rates of preterm births, leading to poorer health outcomes for babies and affecting their long-term well-being, according to a new study.

Black and Hispanic mothers, along with those from lower socioeconomic backgrounds, are particularly at risk of early deliveries following heatwaves.

Extreme heat events are becoming more frequent, lasting longer, and increasing in intensity due to the climate crisis. Last year witnessed record-breaking temperatures, with July 2023 marking the hottest days ever recorded globally for four consecutive days.

Pregnant individuals are especially vulnerable to heat stress, facing higher risks of heat stroke and heat exhaustion, which can adversely affect their unborn babies, according to the CDC.

“The [findings] suggest there are populations that are unable to avoid the heat and are experiencing much bigger effects,” said Lyndsey Darrow, author of the study and professor of epidemiology at the University of Nevada.

Researchers examined 53 million births from 1993 to 2017 across 50 metropolitan areas in the United States. They found that four consecutive days of high heat resulted in a 2% higher chance of preterm births and a 1% increase in early-term births.

“The response is higher in subgroups that you might expect to have less access to air conditioning, and less ability to avoid the heat,” said Darrow.

Preterm birth is the leading cause of infant mortality and is linked to various respiratory and neurodevelopmental issues throughout a child’s life. Heat can induce premature contractions by releasing labor-inducing hormones, reducing blood flow, and causing dehydration, all of which can trigger early labor.

Growing research highlights the need for targeted advice on managing heat stress for expecting mothers. A 2022 study revealed that current guidance on heat exposure for pregnant individuals remains sparse and inconsistent, underscoring the importance of better heat stress management strategies.

“In pregnancy, we err on the side of caution,” said Nathaniel DeNicola, an OB-GYN specialist who authored a 2020 report on air pollution and preterm births.

“There should be extra counselling in clinics and general materials about ways to protect from dehydration and heat stress during times of extreme heat, which is getting more and more common.”



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