Hotter days caused by climate change could put pregnant women at risk of early delivery, according to a new study.

The research, published in the journal Nature Climate Change, found that days with higher temperatures caused an increased delivery risk in women. Less time in the womb for children could lead to health and cognitive issues down the road.

“We estimate that birth rates increase by 5% on days with maximum temperatures above 90 F,” according to the study.

Researchers looked into estimated shifts in daily county birth rates across the U.S. to figure out how much time might be lost during the gestational period when hot days caused earlier births. The data researchers looked at spanned 20 years from 1969 to 1988.

The 20-year sample encompassed 56 million births spanning more than 3 million county days, according to the study.

“We find that extreme heat causes an increase in deliveries on the day of exposure and the following day, and show that the additional births were accelerated by up to two weeks,” the study stated.


The data showed an average of 25,000 infants born earlier because of hot days each year. It resulted in a loss of more than 150,000 gestational days annually, according to the study.

If there is no change, projections show an additional 250,000 gestational days lost per year by the end of the century.

“While we posit climate change will cause gestational losses, the exact magnitude of the future costs is highly uncertain – households may adapt as expectations about the frequency of hot weather events increase, which could mitigate impacts on infant health,” the study stated.