The impact of high ambient temperatures on delivery timing and gestational lengths

Evidence suggests that heat exposure increases delivery risk for pregnant women. Acceleration of childbirth leads to shorter gestation, which has been linked to later health and cognitive outcomes. However, estimates of the aggregate gestational losses resulting from hot weather are lacking in the literature. Here, we use estimated shifts in daily county birth rates to quantify the gestational losses associated with heat in the United States from 1969 to 1988. 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. We estimate that an average of 25,000 infants per year were born earlier as a result of heat exposure, with a total loss of more than 150,000 gestational days annually. Absent adaptation, climate projections suggest additional losses of 250,000 days of gestation per year by the end of the century.