Temperature Extremes May Put Pregnancies at Risk

Very hot and very cold temperatures during pregnancy may increase the risk of preterm birth, say NIH researchers who analyzed records from 223,375 live births at 12 clinical centers.

They linked patients’ electronic records to hourly temperature records for the region surrounding each center. Because “hot” and “cold” can vary depending on the person and place, they defined cold and hot temperatures as below the 10th percentile and above the 90th percentile of average temperatures, respectively.

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Women who experienced extreme cold for the first 7 weeks of their pregnancies had a 20% higher risk of delivering before 34 weeks, a 9% higher risk of delivering between 34 and 36 weeks, and 3% higher risk of delivering in weeks 37 and 38.

But the researchers found more consistent associations with early delivery after exposure to extreme heat than extreme cold. Overall, exposure to extreme heat for the duration of pregnancy was associated with increases in risk for delivery at 34 weeks and 36 to 38 weeks by 6% to 21%. The researchers suggest that during cold spells, people are more likely to seek shelter and get warm—and may be more likely to just endure hot weather.

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The researchers theorize that the stress of temperature extremes could hinder the development of the placenta or alter blood flow to the uterus, both of which could lead to early labor.