Heat Stress and Birth Outcomes in a Pregnancy Cohort in RuralAmhara, Ethiopia

Abstract

Background: Prenatal extreme heat exposure is associated with increased incidence of adversepregnancy outcomes including preterm birth, low birthweight, and miscarriage. However, fewstudies have investigated the ramifications of prenatal heat exposure in low- and middle-incomecountries such as Ethiopia, which ranks 15th on the UNICEF Children's Climate Risk Index.

Objective: To assess associations between pre-conception and prenatal heat exposure and birthoutcomes including anthropometric z-scores, gestational age, preterm birth and stillbirth.

Design/Methods: We conducted secondary analysis of data from the Enhancing Nutrition andAntenatal Infection Treatment study, a randomized clinical effectiveness trial that enrolled 2392patients at < 24 weeks gestation at 12 health centers in rural Amhara, Ethiopia from August 2020to July 2022. Pregnancies were followed until 1 month postpartum. Daily wet bulb globetemperature (WBGT) was approximated based on the individual's place of residence or antenatalcare center with MODIS-Aqua satellite land surface temperature data (1:30pm) and GlobalForecasting Systems relative humidity data (12pm), using the Stull's equation. We averaged dailyWBGT by trimester, overall pregnancy, and the 6-month pre-conception period for each pregnancy. We used linear and logistic regression to examine associations between heatexposure and continuous and dichotomous outcomes, respectively, adjusting for relevantcovariates.

Results: Birth anthropometrics: Increased first and third trimester and overall pregnancy WBGTwere associated with decreased birth head circumference-for-age z-score (T1 effect size -0.032cm per 1°C increase, 95% CI -0.050 to -0.014; T3 -0.019, 95% CI -0.037 to -0.000; and overallpregnancy -0.033, 95% CI -0.060 to -0.006). There were no associations between WBGT andweight- and length-for-age z-scores. Gestational age: Increased pre-conception WBGT wasassociated with lower gestational age (-0.039 weeks per 1°C increase, 95% CI -0.074 to -0.004).Preterm birth: Increased third trimester WBGT was associated with increased odds of pretermbirth (odds ratio of 1.067 per degree increase, 95% CI 1.017 to 1.120). Stillbirth: We found nosignificant association between heat exposure and stillbirth.

Conclusion(s): Infants born to mothers with increased pre-pregnancy or prenatal heat exposurewere born at younger gestations and with lower head circumference-for-age z-scores. Furtherstudies are needed to better characterize heat exposures and associated pregnancy outcomesand neurodevelopment in climate-vulnerable countries such as Ethiopia.