Associations between ambient temperature and pregnancy outcomes from three south Asian sites of the Global Network Maternal Newborn Health Registry: A retrospective cohort study

Abstract

Objective: Growing evidence suggests that environmental heat stress negatively influences fetal growth and pregnancy outcomes. However, few studies have examined the impact of heat stress on pregnancy outcomes in low-resource settings. We combined data from a large multi-country maternal-child health registry and meteorological data to assess the impacts of heat stress.

Design: Retrospective cohort study.

Setting: Three sites based in south Asia as part of the Global Network for Women's and Children's Health research in India (Belagavi and Nagpur) and Pakistan (Thatta).

Population or sample: Data from women enrolled between 2014 and 2020 in the Global Network's Maternal Newborn Health Registry (MNHR), a prospective, population-based registry of pregnancies, were used.

Methods: A total of 126 273 pregnant women were included in this analysis. Daily maximal air temperatures (T_max ) were acquired from local meteorological records. Associations between averages of daily maximal temperatures for each trimester and main outcomes were analysed using a modified Poisson regression approach.

Main outcomes measures: Incidence of stillbirth, preterm birth, low birthweight (<2500 g) or evidence of pregnancy hypertension or pre-eclampsia.

Results: In the overall cohort, risk of preterm birth was positively associated with greater temperature in the second trimester (relative risk [RR] 1.05, 95% CI 1.02-1.07, p = 0.0002). Among individual sites, the risk of preterm birth was greatest in Nagpur (RR 1.07, 95% CI 1.03-1.11, p = 0.0005) and associated with second-trimester temperature. The overall risk of low birthweight was associated with ambient temperature in second trimester (RR 1.02, 95% CI 1.01-1.04, p = 0.01). The risk for LBW was associated with first-trimester heat in Thatta and with second-trimester heat in Nagpur. Finally, the overall risk of gestational hypertensive disease was associated with greater temperature in the third trimester among all sites (RR 1.07, 95% CI 1.02-1.12, p = 0.005) and was particularly significant for Nagpur (RR 1.13, 95% CI 1.05-1.23, p = 0.002). These findings highlight the increased risk of detrimental obstetric and neonatal outcomes with greater temperature.

Conclusion: In a multi-country, community-based study, greater risk of adverse outcomes was observed with increasing temperature. The study highlights the need for deeper understanding of covarying factors and intervention strategies, especially in regions where high temperatures are common.

Keywords: climate change; heat stress; low birthweight; pre-eclampsia; pregnancy; stillbirth.

Figure 1.

Participant flow diagram showing selection of the analytical cohort.

Figure 2.

Average daily maximal temperatures for summarized by month for the study duration for the three study sites.

Figure 3.

Relative risks for the incidence of (A) stillbirth; (B) preterm birth; (C) gestational hypertensive disease; and (D) low-birth weight for the combined cohort. Relative risks with corresponding 95% CI and p-values obtained from modified Poisson approach with a sandwich estimator for each categorical outcome and 5-degree Celsius change in trimester average daily maximum temperatures. Models include site and site by outcome interaction. Site-specific relative risks were derived from the site by outcome interaction and are presented in supplementary figures.