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

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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.

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Fig. 1: Temperature–dose response function on day 0.
Fig. 2: Effect of daily maximum temperature ≥90 °F on birth rates by days from exposure.
Fig. 3: Heterogeneous effects of daily maximum temperature ≥90 °F on birth rates, cumulative effects by days from exposure.
Fig. 4: Effect of daily maximum temperature ≥90 °F relative to 60–70 °F on birth rates, interacted with air conditioning.

Data availability

All data necessary for replication of the results in this paper are available for download at The original weather data can be downloaded from The original birth records can be downloaded from The population data can be downloaded from Interested researchers should contact Urs Beyerle or Jan Sedlacek at ETH Zurich to gain access to the CMIP5 climate projection data. Source data for Figs. 1–4 are provided with the paper.

Code availability

The code necessary for replication of the results in this paper is available for download at


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We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups for producing and making available their model output. We are grateful for U. Beyerle and J. Sedlacek at ETH Zurich, who provided access to the CMIP data. This research was supported by funding from the California Strategic Growth Council Climate Change Research Program (no. CCRP0056). P. Stainier provided valuable research assistance.

Author information

A.B. and J.S. designed the research, interpreted the data and wrote the paper. A.B. analysed the data.

Correspondence to Alan Barreca.

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Supplementary information

Source data

Source Data Fig. 1

Temperature-Dose Response Function on Day 0

Source Data Fig. 2

Effect of Daily Maximum Temperature ≥90 °F on Birth Rates, by Days from Exposure. a: Distributed lag coefficients; b: cumulative effects

Source Data Fig. 3

Heterogeneous Effects of Daily Max Temperature ≥90 °F on Birth Rates

Source Data Fig. 4

Modifying effect of air conditioning

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Barreca, A., Schaller, J. The impact of high ambient temperatures on delivery timing and gestational lengths. Nat. Clim. Chang. (2019) doi:10.1038/s41558-019-0632-4

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