Hot weather due to climate change is linked to early childbirth in the U.S., a new study released Monday suggests.
The study said that hot temperatures cause women to have shorter pregnancies than they normally would, which could pose risks for infant health and child development.
Specifically, birth rates were 5% higher on days when the temperature was above 90 degrees, according to a statement released by the University of California – Los Angeles. “And, perhaps more concerning, births on those days occurred up to two weeks earlier – and 6.1 days earlier on average – than they would have otherwise,” the statement said.
“That’s enough to take somebody from what’s considered to be a pretty healthy pregnancy into a ‘we are somewhat worried’ pregnancy,” said Alan Barreca, a UCLA professor of environment and human health and lead author of the new study.
The study was published in the peer-reviewed British journal Nature Climate Change.
Researchers looked at past birth and temperature data and estimated that about 25,000 babies were born prematurely each year between 1969 and 1988 due to hot weather.
The key finding was that birth rates spiked right around the days the temperature exceeded 90 degrees. After the hot weather passed, birth rates fell.
This pattern indicates that hot weather accelerates deliveries and shortens pregnancies, Barreca said.
Rising temperatures and heat waves are one of the clearest signs of human-caused climate change: By the end of the century, the National Climate Assessment estimates there will be up to 30 additional days over 90 degrees each year in the U.S., the Guardian said, unless we reduce the emissions of greenhouse gases that cause global warming.
It’s not clear why babies are born earlier when it’s hot, the study said, but researchers say high heat can bring cardiovascular stress, which can induce pregnancy, Time reported. In addition, heat increases the levels of oxytocin, a hormone that plays a role in labor.
Barreca said air conditioning could reduce the effects of climate change on pregnancies, but class and racial disparities can prevent some women from having access to air conditioning.
Mitchell Kramer, the chair of obstetrics and gynecology at Northwell Health’s Huntington Hospital in New York, who was not involved in the study, told HealthDay, “More study needs to be done, but certainly we must help protect pregnant women from extremes of heat as well as work on the causes of climate change.”