Climate change has increased global annual temperatures by approximately 1·2°C compared with pre-industrial temperatures. Studies have shown that there is an increased risk of adverse birth outcomes in mothers who are exposed to high ambient temperatures, including premature birth, low birthweight, stillbirth, and gestational diabetes (
During pregnancy, the effects of heat stress, which is defined as the environmental exposure of heat, humidity, solar radiation, and wind speed, while heat strain is defined as the physiological response to that stress are exacerbated by an increased physiological demand from the fetus and placenta. Hypotheses from animal and human fever studies speculate that raised core temperature, dehydration, reduced uterine blood flow, inflammatory changes, and heat shock proteins could be involved (3✔ ✔Trusted Source
ASAS-SSR Triennnial Reproduction Symposium: Looking Back and Moving Forwardâ”How Reproductive Physiology has Evolved: Fetal origins of impaired muscle growth and metabolic dysfunction: Lessons from the heat-stressed pregnant ewe1
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The study involved 92 pregnant subsistence farmers in Gambia and is the first to measure the impacts of heat stress on the fetuses of manual workers.
Relationship Between Heat and Fetal Strain
Researchers found that for every degree Celsius increase in heat stress exposure, there was a 17% increase in fetal strain, as indicated by raised fetal heart rate and slower blood flow through the umbilical cord. It is also seen that even a modest rise in body temperature from performing manual tasks in extreme heat produced evidence of physiological strain in both mother and fetus.
For the study, participants were encouraged to perform their usual daily tasks during field visits and were fitted with a wearable device to record maternal heart rate, skin temperature, and estimated energy expenditure.
Portable ultrasound devices were used to record fetal heart rate, umbilical artery blood flow at the start of each visit (used as the baseline), at a mid-point during a worker’s shift, and then at the end of the shift.
Maternal symptoms of heat illness were also collected. Nausea, vomiting, headache, dizziness, weakness, muscle ache, fatigue, and dry mouth, were common among participants, with over half of the women reporting that they experienced at least one symptom during field visits.
“Climate change has led to increasingly extreme temperatures worldwide and Sub-Saharan Africa is particularly vulnerable to climate impacts. The study found that pregnant subsistence farmers in The Gambia commonly experience levels of extreme heat above recommended outdoor working limits, and that this can have significant effects on their health and the health of their babies. The results suggest we have to find effective interventions to protect these women and reduce adverse birth outcomes”, said researchers.
Analysis of the data showed strong links between heat stress exposure and maternal heat strain, which was also found to be associated with fetal strain. Maternal heat stress was also strongly linked to fetal strain even when controlling for maternal heat strain, indicating that other biological factors need to be considered.
The findings also highlight the need for further work to identify and evaluate interventions that will help pregnant agricultural workers working in extreme heat.
- Environmental heat stress on maternal physiology and fetal blood flow in pregnant subsistence farmers in The Gambia, west Africa: an observational cohort study – (https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(22)00242-X/fulltext)
- Association of Air Pollution and Heat Exposure With Preterm Birth, Low Birth Weight, and Stillbirth in the US
- ASAS-SSR Triennnial Reproduction Symposium: Looking Back and Moving ForwardHow Reproductive Physiology has Evolved: Fetal origins of impaired muscle growth and metabolic dysfunction: Lessons from the heat-stressed pregnant ewe1
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