An expert review of environmental heat exposure and stillbirth in the
face of climate change: clinical implications and priority issues
Abstract
Exposure to extreme heat in pregnancy increases the risk of stillbirth.
Progress in reducing stillbirth rates has stalled, and populations are
increasingly exposed to high temperatures and climate events that may
further undermine health strategies. This narrative review summaries the
current clinical and epidemiological evidence of the impact of maternal
heat exposure on stillbirth risk. 19 out of 20 studies found an
association between heat and stillbirth risk. Recent studies based in
low- middle- income countries and tropical settings add to the existing
literature to demonstrate that all populations are at risk.
Additionally, both short-term heat exposure and whole-pregnancy heat
exposure increase the risk of stillbirth. A definitive threshold of
effect has not been identified, as most studies define exposure as
> 90 th percentile of the usual
temperature for that population. Therefore, the association between heat
and stillbirth has been found with exposures from as low as
>12.64°C up to >46.4°C. The pathophysiological
pathways by which maternal heat exposure may lead to stillbirth, based
on human and animal studies, include both placental and embryonic or
fetal impacts. Although evidence gaps remain and further research is
needed to characterise these mechanistic pathways in more detail,
preliminary evidence suggests epigenetic changes, alteration in
imprinted genes, congenital abnormalities, reduction in placental blood
flow, size and function all play a part. Finally, we explore this topic
from a public health perspective; we discuss and evaluate the current
public health guidance on minimising the risk of extreme heat in the
community. There is limited pregnancy specific guidance within heatwave
planning, and no evidence-based interventions have been established to
prevent poor pregnancy outcomes. We highlight priority research
questions to move forward in the field and specifically note the urgent
need for evidence-based interventions that are sustainable.