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### **Impact of Heat Stress on Pregnant Subsistence Farmers in West Africa**

**Ana Bonell1, Bakary Sonko1, Jainaba Badjie1, Tida Samateh1, Tida Saidy1, Fatou Sosseh1, Yahya Sallah1 , Kebba Bajo1, Kris A. Murray1,2,3, Jane Hirst4, Ana Vicedo-Cabrera5,6, Andrew M. Prentice1, Neil S. Maxwell7, and Andy Haines2**

1Medical Research Council Unit, Gambia, London School of Hygiene and Tropical Medicine, Fajara, Gambia 2Centre on Climate Change and Planetary Health, London School of Hygiene and Tropical Medicine, London, UK

3MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, UK

<sup>4</sup>Nuffield Department of Women's and Reproductive Health and the George Institute for Global Health, University of Oxford, Oxford, UK

<sup>5</sup> Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland

6Oeschger Center for Climate Change Research, University of Bern, Bern, Switzerland

7Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK

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 the 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. This observational cohort study utilized the high heat stress in West Africa to gain an 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. 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 modeling 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.

Ana Bonell1, Bakary Sonko1, Jainaba Badjie1, Tida Samateh1, Tida Saidy1, Fatou Sosseh1, Yahya Sallah1, Kebba Bajo1, Kris A. Murray1,2,3, Jane Hirst4, Ana Vicedo-Cabrera5,6, Andrew M. Prentice1, Neil S. Maxwell7, and Andy Haines2


#### Introduction

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 the 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.

#### Methods

This observational cohort study utilised high heat stress in West Africa to gain an 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, and environmental measurements, maternal physiology (e.g. heat strain) and fetal stress (fetal heart rate > 160 or < 115, or increase in umbilical artery resistance index)

#### 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). Multilevel model of fetal stress.



*UTCI = universal thermal climate index; PSI = physiological strain index; TBW = total body water*

Decreasing maternal exposure to heat stress in later pregnancy may reduce fetal stress, a potential pathophysiological mechanism leading to adverse birth outcomes. However, there remain large evidence gaps in relation to the pathophysiology of heat in pregnancy, the identification of those at risk and the development of suitable and effective interventions to reduce adverse birth outcomes. Further work exploring changes in placental blood flow and the association with pregnancy outcomes is urgently needed, in a variety of settings and populations. In addition, co-development and trials of interventions in pregnant subsistence farmers in SSA would be a welcome and exciting area to explore.

#### Mean change in fetal heart rate

Schematic representation of physiological responses to thermal factors, and measurements taken at each field visit to quantify these factors in grey.

Mean change in fetal heart rate from cool baseline to heat-exposed work environment.

#### References

Watts N, Amann M, Arnell N, Ayeb-Karlsson S, Beagley J, Belesova K, et al. The 2020 report of The Lancet Countdown on health and climate change: responding to converging crises. Lancet. 2021;397(10269):129-70.

Chersich MF, Pham MD, Areal A, Haghighi MM, Manyuchi A, Swift CP, et al. Associations between high temperatures in pregnancy and risk of preterm birth, low birth weight, and stillbirths: systematic review and meta-analysis. BMJ. 2020;371:m3811.

Improving Health Worldwide • www.lshtm.ac.uk

Bonell A, Hirst J, Vicedo-Cabrera AM, Haines A, Prentice AM, Maxwell NS. A protocol for an observational cohort study of heat strain and its effect on fetal wellbeing in pregnant farmers in The Gambia. Wellcome Open Res. 2020;5:32.

Bonell A; Bakary S; Badjie, J; Samateh, T; Saidy, T; Sosseh, F; Sallah, et al. Assessing the Effect of Environmental Heat Stress on Maternal Physiology and Fetal Blood Flow in Pregnant Subsistence Farmers in West Africa. PREPRINT. 2021.
