The team led by researchers at the Medical
Research Council (MRC) Unit The Gambia at the London School of Hygiene &
Tropical Medicine (LSHTM) and LSHTM found that even a modest rise in body
temperature from performing manual tasks in extreme heat produced evidence of
physiological strain in both mother and foetus.
Findings include that for every degree Celsius
increase in heat stress exposure there was a 17% increase in foetal strain as
indicated by raised foetal heart rate and slower blood flow through the
umbilical cord.
The research is published in The Lancet
Planetary Health.
The foetuses of women working in the fields in
extreme heat can show signs of strain before their mothers are affected the
research has shown.
The study, which involved 92 pregnant
subsistence farmers in The Gambia, is the first to measure the impacts of heat
stress on the foetuses of manual workers.
Dr Ana Bonell, Wellcome Trust Global Health
Clinical PhD Fellow at LSHTM and lead author, said: “Climate change has led to
increasingly extreme temperatures worldwide and Sub-Saharan Africa is
particularly vulnerable to climate impacts. Our 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.”
Study author Jainaba Badjie from MRC The
Gambia at LSHTM said: “Despite the growing scientific evidence linking maternal
heat exposure to adverse birth outcomes, including premature birth, low birth
weight, and still birth, up until now there has been little research into the
physiological mechanisms responsible for these outcomes. We urgently need to
understand these mechanisms so that we can find better ways to support mothers
and babies in these conditions.”
For the study, participants in West Kiang, The
Gambia, 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 foetal 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.
Analysis of the data showed strong links
between heat stress exposure and maternal heat strain, which was also found to
be associated with foetal strain. Maternal heat stress was also strongly linked
to foetal strain even when controlling for maternal heat strain, indicating
that other biological factors need to be considered.
The researchers suggest that an important
physiological factor to consider in future work is the diversion of blood from
the placenta to the skin which appears to occur at lower core temperatures than
highlighted by previous studies. The findings also highlight the need for
further work to identify and evaluate interventions that will help pregnant
agricultural workers in Sub-Saharan Africa to adapt to working in extreme
heat.
Reference:
Dr Ana Bonell et al, A cohort study assessing
the effect of environmental heat stress on maternal physiology and fetal blood
flow in pregnant subsistence farmers in The Gambia, West Africa, JOURNAL The Lancet Planetary Health