Assessing the Effect of Environmental Heat Stress on Maternal Physiology and Fetal Blood Flow in Pregnant Subsistence Farmers in West Africa

Background: Anthropogenic climate change has led to increasingly extreme temperatures worldwide. Sub-Saharan Africa (SSA), including West Africa, is considered especially vulnerable to the impacts of climate extremes. In SSA women make up 50% of agricultural workforce and often work throughout pregnancy, while maternal exposure to high temperatures increases the risk of adverse birth outcomes. Understanding the physiological mechanisms responsible is central to designing targeted interventions to reduce the risks of heat exposure. Method: This observational cohort study utilised the high heat stress in West Africa to gain understanding of the physiological impact of heat on maternal and fetal physiology. Pregnant subsistence farmers who performed manual tasks throughout pregnancy were observed during field visits where environmental measurements, maternal physiology (e.g. heat strain) and fetal stress (fetal heart rate > 160 or < 115, or increase in umbilical artery resistance index) were measured. Results: A total of 92 participants were included (122 field visits). Extreme heat stress was observed in 31% of field visits. Maternal temperature, heat strain and fetal heart rate were all significantly increased from baseline to working. Fetal stress occurred in 41/122 (33%) field visits. Multilevel modelling revealed that fetal stress was significantly associated with both Universal Thermal Climate Index (OR 1·17, CI 1·05;1·29, p=0.01) and gestational age (OR 1·12, CI 1·02;1·22, p=0.02). Interpretation: Decreasing maternal exposure to heat stress in later pregnancy may reduce fetal stress, a potential pathophysiological mechanism leading to adverse birth outcomes. There is an urgent need to explore this further. Funding Information: This project was funded by the Wellcome Trust through the Wellcome Trust Global Health PhD Fellowship awarded to AB (216336/Z/19/Z). Declaration of Interests: None declared. Ethics Approval Statement: The study was approved by the Gambia government/MRC Joint ethics committee and the London School of Hygiene and Tropical Medicine Ethics Advisory Board (ref: 16405) in accordance with the Declaration of Helsinki (2013).