Association of Summer Heat Waves and the Probability of Preterm Birth in Minnesota: An Exploration of the Intersection of Race and Education.

Preterm birth (PTB) is common and has negative impacts on infant health. While some maternal risk factors have been identified, including age under 20 or over 40, substance abuse, low BMI, and racism, less is known about the impact of environmental exposures like high heat. We combined 154,157 records of live births occurring in Minnesota between 2009 and 2015 with hourly weather records collected from the Minneapolis-St. Paul airport. We tested if maternal heat wave exposure (a seven-day period with a mean daily high temp of 37 °C) immediately prior to birth leads to a higher risk of preterm birth. Additional covariates included maternal age, race/ethnicity, educational status, and residence in the seven-county Minneapolis-St. Paul metro area. Pregnant women exposed to a seven-day heat wave of 37 °C or higher experienced a higher relative risk of PTB compared to women who did not experience a heat wave (1.14 risk ratio (RR), 1.0-1.3 95% confidence interval (CI)). The result is robust to controls for a woman's age, race/ethnicity, educational attainment, place of residence, and year of the birth. Children born to Black women with college degrees who are exposed to heat waves experience a higher relative risk of PTB compared to White women with college degrees in a heat wave (2.97 RR, 1.5-6.1 95% CI). Summer heat waves are associated with higher risk of PTB in late-term pregnancies in Minnesota.