Early delivery of singleton pregnancies may be impacted by both acute and chronic ambient temperature extremes, a new study found. Researchers examined medical records from 223,375 singleton deliveries from 12 US sites linked to local ambient temperature. Acute temperature associations were estimated separately for warm (May-September) and cold season (October-April) in a case-crossover analysis. They found:
• Exposure to hot or cold temperatures during weeks 1 to 7 increased risk for early preterm, late preterm, and early term delivery when compared with mild temperature.
• Results were similar for hot exposures during weeks 15 to 21.
• Whole-pregnancy hot exposures increased delivery risk by 6% to 21% at weeks 34 and 36 to 38.
• A 5°F increase during the week preceding delivery was associated with 12% to 16% higher and 4% to 5% lower early delivery risk during warm and cold season, respectively.
Citation: Ha S, Liu D, Zhu Y, Kim S, Sherman S, Mendola P. Ambient temperature and early delivery of singleton pregnancies. [Published online ahead of print August 31, 2016]. Environ Health Perspect. doi:10.1289/EHP97.