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

Abstract

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.

Acute associations between heatwaves and preterm and early-term birth in 50 US metropolitan areas: a matched case-control study

“…We observed that heatwaves were more strongly associated with both early-term and preterm birth among non-Hispanic black and Hispanic mothers. These findings are in-line with those from previous studies [ 31 , 47 , 48 ]. Minority groups might be more vulnerable to heatwave events due to a lack of a cooling system in the household and less access to neighborhood greenness.…”

Effect of Elevated Ambient Temperature on Maternal, Foetal, and Neonatal Outcomes: A Scoping Review

“…Nine studies employed apparent temperature (combined effect of air temperature and relative humidity) to identify the exposure effects on elevated ambient temperatures on pregnant women and neonates [11,12,[32][33][34][35][36][37][38]. Twelve studies examined the effects of heatwaves/extreme heat events on maternal, foetal, and neonatal outcomes [6,32,[38][39][40][41][42][43][44][45][46][47]. They used different heatwave characteristics, i.e., length of exposure, threshold percentile (75th, 90th, 95th, and 98th percentile to identify high temperatures), peak temperature, and a number of heatwaves/heat events, to estimate the magnitude of the exposure effects [6,32,[38][39][40][41][42][43][44][45][46][47].…”

“…Twelve studies examined the effects of heatwaves/extreme heat events on maternal, foetal, and neonatal outcomes [6,32,[38][39][40][41][42][43][44][45][46][47]. They used different heatwave characteristics, i.e., length of exposure, threshold percentile (75th, 90th, 95th, and 98th percentile to identify high temperatures), peak temperature, and a number of heatwaves/heat events, to estimate the magnitude of the exposure effects [6,32,[38][39][40][41][42][43][44][45][46][47]. No consistent definition for 'heatwave' or 'extreme heat event' was observed among reviewed studies.…”

“…No consistent definition for 'heatwave' or 'extreme heat event' was observed among reviewed studies. Trimester-specific exposures Trimester-specific temperature 3 [75,76,94] Apparent temperature exposure Apparent temperature index 1 [32] Daily maximum apparent temperature (MAT) 2 [11,33] Mean apparent daily temperature 5 [12,[34][35][36][37] Mean apparent weekly temperature 1 [35] Mean apparent monthly temperature 1 [35] Universal apparent maximum temperature (UATmax) 1 [38] Heatindex/Heatwave/ Extreme heatevents exposure Wet-bulb globe temperature (WBGT) 1 [95] Dry temperature 2 [44,58] Wet temperature 1 [58] Mean heat index (HI) 1 [59] Heatwave/extreme heat events 12 [6,32,[38][39][40][41][42][43][44][45][46][47] Note: Some studies examined exposure effects using multiple temperature metrics.…”

“…Elevated Ambient Temperature-Associated Adverse Neonatal Outcomes Preterm Birth (PTB) Among the 75 studies examined, PTB was the most common adverse outcome (n = 30) observed in this review. Among these, 23 studies reported that elevated temperatures significantly correlate with an increased risk or rate of preterm birth [11][12][13]32,33,39,43,44,46,50,52,56,58,59,61,63,65,69,77,79,80,92,93]. For instance, a time-series study conducted in Iran reported a significant increase in PTB risk from heatwave days (mean daily temperature > 90th percentile ≥ 2 consecutive days) compared to non-heatwave days (RR 1.21; 95%CI 1.08: 1.37) [32].…”