A new study has found that heatwaves significantly increase the rate of preterm births, leading to poorer health outcomes for babies and impacting their long-term well-being. The research highlights that Black and Hispanic mothers, along with those from lower socioeconomic backgrounds, are particularly vulnerable to delivering early after experiencing extreme heat events.
The frequency of extreme heat events, their duration, and intensity are escalating due to the ongoing climate crisis. Last year, record-breaking temperatures were recorded globally, with July 2023 marking the hottest days ever documented for four consecutive days.
According to the Centers for Disease Control and Prevention (CDC), pregnant people are among the most susceptible to heat stress, which raises their risk of heat stroke and heat exhaustion. These conditions can negatively affect unborn babies, further underlining the vulnerability of expectant mothers during extreme heat.
“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.
The researchers examined 53 million births between 1993 and 2017 across 50 metropolitan areas in the United States. Researchers discovered a 2% higher chance of premature births and a 1% increase in early-term births following four consecutive days of high heat.
“The response is higher in subgroups that you might expect to have less access to air conditioning and less ability to avoid the heat,” Darrow said.
Preterm birth is the leading cause of infant mortality and is linked to a variety of respiratory and neurodevelopmental outcomes throughout a child's life. Heat can induce premature contractions by triggering the release of labor-inducing hormones, reducing blood flow, and causing dehydration, which can lead to early labor.
Emerging research highlights the necessity of providing targeted advice on managing heat stress for expecting people. A 2022 study found the lack and inconsistency of current guidance on heat exposure for pregnant people.
“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 counseling 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.”
