Increased Exposure To Hot Weather May Be Causing Women To Give Birth Earlier, Study Suggests

Birth rates increased by 5 percent on days with a maximum temperature above 32.2°C (90°F). Ton Weerayut Photographer/Shutterstock

Exposure to hotter temperatures may cause as many as 25,000 early births in the US every year. As global temperatures continue to consistently increase around the world, new research suggests that this number will rise by the end of the century if proactive measures aren’t taken.

Previous evidence suggests that increased heat exposure can increase the delivery risk for pregnant women potentially due to how higher temperatures affect oxytocin, a key hormone in regulating the onset of delivery, or put stress on the cardiovascular system – both of which may induce labor.

To determine the risk of early delivery in correlation with warmer temperatures, researchers at the University of California, Los Angeles estimated shifts in daily birth rates from counties across the US over 20 years of data from 1969 to 1988. Exposure to extreme heat causes a “large increase” in delivery risk with as many as 56 million births spanning more than 3 million days.

Birth rates increased by 5 percent on days with a maximum temperature above 32.2°C (90°F) and the average birth was given six days early, with some occurring up to two weeks before the delivery date.

“We find that extreme heat causes an increase in deliveries on the day of exposure and on the following day and show that the additional births were accelerated by up to two weeks,” wrote the authors in Nature Climate Change. “We estimate that an average of 25,000 infants per year was born earlier as a result of heat exposure, with a total loss of more than 150,000 gestational days annually.”

Exposure to hotter weather as a result of climate change may harm infant health. Previous research has suggested a link between shorter gestational periods and negative health and cognitive outcomes later in life. Previous research has not quantified exactly how many days of gestation are lost due to weather, but the researchers predict that an additional 250,000 gestational days could be lost every year by the end of the century if nothing is done to tackle climate change.

“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,” write the authors, adding that though access to air conditioning is an “effective adaptation strategy” likely to be increasingly employed, it may also increase greenhouse gas emissions associated with risks to fetal development.

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