New research by CMC Prof. Jessamyn Schaller suggests that hot weather due to climate change is causing shorter pregnancies, which poses risks to infant health and child development.
The research published in Nature Climate Change this month found that birth rates were 5 percent higher when temperatures topped 90 degrees. In addition, births on those days occurred up to two weeks earlier — or 6.1 days earlier on average — than they would have otherwise.
“Absent adaptation, climate projections suggest additional losses of 250,000 days of gestation per year by the end of the century,” said Schaller, whose research focuses on economic conditions’ effects on child welfare. “Given recent increases in the frequency of extremely hot weather, there is a clear need to better forecast the potential magnitude of climate change’s impact on infant health at the national level.”
Schaller and a coauthor analyzed U.S. birth and climate statistics from 1969 to 1988, using natality information from the National Vital Statistics System and data from the Global Historical Climatology Network. They matched county-level birth rates to local weather patterns and examined how unpredictable changes in the weather altered the timing of births.
They found that county birth rates were higher on hot days, and then lower from 2-14 days after heat exposure. “The spike-then-fall pattern in birth rates indicates that hot weather accelerates deliveries and shortens pregnancies,” said Schaller.
One possible reason for this, Schaller said, is heat increases levels of oxytocin, a key hormone regulating the onset of delivery. Alternatively, extreme heat might cause earlier deliveries via cardiovascular stress or sleep disruption.
By the year 2100, the study estimates, an additional 42,000 births will be affected per year, or about one out of every 100 births.
“Our research adds a big piece to the puzzle about the impacts of heat exposure on birth and infant outcomes. In addition to expanding our understanding of the potential effects of climate change on maternal and infant health, our findings suggest that pregnant women who are entering the third trimester should avoid exposure to extreme heat,” said Schaller.