Research shows high temperatures can trigger premature labor in women—a risk poised to rise with climate change.
Spanish researchers from Barcelona University Hospital reported in 2013 that temperatures exceeding 30°C accelerate childbirth, based on nearly 8,000 births. A newer study in Nature Climate Change confirms this, finding that U.S. temperatures above 32°C may cause thousands of premature births annually.
University of California researchers analyzed birth rates across U.S. counties over 1969 to 1988, covering about 56 million births. They found birth rates rose an average of 5% on days with maximum temperatures over 32.2°C. Deliveries occurred on average six days earlier, with some up to two weeks before term.
“We find that high heat leads to an increase in deliveries on the day of exposure and the following day, and that additional births have been accelerated by up to two weeks,” the researchers explain. “We estimate that an average of 25,000 infants per year are born earlier due to heat exposure, with a total loss of over 150,000 gestational days per year.”
High heat likely affects oxytocin, which regulates labor onset, and stresses the cardiovascular system, potentially inducing early delivery.
Preterm births often lead to more medical issues and higher hospital costs for infants. With climate projections in mind, experts urge better forecasting of global warming's impact on newborn health.
Lead author Alan Barreca highlights the issue: “We predict that more than one in 100 births will occur earlier than expected in the United States by the end of the century. This number may seem small, but it is much higher than the chances of having a car accident.”
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