An average of 25,000 infants per year were born earlier as a result of hot weather, with a loss of more than 150,000 gestational days annually in the United States from 1969 to 1988, suggests a paper published in Nature Climate Change. Hot weather can cause an increase in deliveries on the day of exposure, with births occurring up two weeks early.
Increased exposure to hot weather due to climate change is likely to harm infant health, though the scale of this threat has not been well documented. Shorter gestational periods have been linked to negative health and cognitive outcomes later in life. Previous research suggests that hot weather leads to an acceleration of childbirth and shorter gestations. However, it is unknown exactly how many days of gestation are lost due to hot weather.
Alan Barreca and Jessamyn Schaller used estimated shifts in daily birth rates from counties across the United States to quantify the total number of lost days of gestation associated with heat over a span of 20 years. The authors’ sample included 56 million births spanning more than 3 million county-days. They estimate that birth rates increase by five percent on days with a maximum temperature above 90°F (32.2°C), with an average gestational reduction of 6.1 days. Some births occurred two weeks early.
The authors conclude that, according to climate projections, an additional 250,000 gestational days could be lost annually by the end of the century.
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