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A growing body of research suggests links between extreme heat and adverse pregnancy outcomes.
Like many other parts of the world, Kilifi – a largely hot and humid county along Kenya’s coast – is grappling with the devastating effects of climate change and deforestation.1 Rising air temperatures, recurring flash floods, and prolonged droughts are now frequent in this semi-arid region, threatening food security2 and affecting human health3.
“Sometimes it’s very, very hot,” says Kenneth Miriti, the county’s reproductive health coordinator, and there’s little respite from the heat at night, he adds. Poorly ventilated houses make the problem worse.
Among those particularly vulnerable are pregnant people.
For nearly a decade, Miriti has seen many miscarriage cases and pregnancy complications due to the high prevalence of anaemia in the region, lack of access to clean water, poor health education and access to care. But only recently has his team begun to make connections between adverse maternal health outcomes and higher-than-usual temperatures in the region. “We as healthcare providers had never thought of heat as one of the contributing factors,” Miriti says.
In 2021, Miriti participated in a study4 that documented the perspectives of public health officials, community healthcare workers and leaders, and pregnant women and their family members on how extreme heat in Kilifi was impacting mother and child health. While pregnant women described experiencing heat exhaustion including feeling dehydrated, dizzy, fatigued, and irritable, Miriti pointed to the discomfort pregnant patients felt when visiting healthcare facilities that lacked cooling.
Researchers across the globe are finding that extreme heat increases the likelihood of babies being born early and weighing less than 2,500 grams5, the threshold below which newborns may experience health complications. Exposure to rising temperatures can also heighten stillbirth risks, where a baby could die in the womb at or after 20 weeks of pregnancy.6
“That concerns me a lot,” says Lisa Patel, a paediatric hospitalist at Stanford HealthCare Tri-Valley hospital. She worked two of her busiest shifts in the summer of 2022, attending to pregnancy complications when record-breaking heatwaves hit large parts of California. “With the number of hot days increasing, it is something all obstetricians and gynaecologists should know about in terms of caring for their pregnant patients.”
While sweltering heat can affect all people, it’s especially dangerous for pregnant women.
Their body already works hard to maintain a normal core temperature, but to cool down in very hot conditions requires much harder work. That means pregnant people are at a greater risk of dehydration and heat strokes.7
Scientists expect pregnancy outcomes to be worse when humidity accompanies high temperatures. The high humidity makes it more difficult for sweat to evaporate, so the body’s natural cooling system doesn’t work as well.
“If you overheat very early in conception, you can risk having a birth defect in your child,” says Sari Kovats, an environmental epidemiologist at the London School of Hygiene and Tropical Medicine. “That’s why pregnant women are told not to go to a sauna.”
As temperatures rise, more blood flows close to the skin to initiate heat loss, but this can cause a reduction in blood flow to the placenta.8 Consequently, the foetus may not receive sufficient oxygen and nutrients, which can restrict the baby’s growth or trigger early labour. Inadequate placental blood flow could also induce another complication called preeclampsia, a high blood pressure condition that develops during pregnancy and may be dangerous for both the mother and baby.9
In a study involving pregnant farm-working women in rural Gambia who frequently experienced extreme heat, early findings indicated reduced blood flow to the placenta and higher-than-normal foetal heart rates.10 The researchers estimated a 17 percent increase in the risk of such foetal strain for every 1°C rise in temperature, while calling for more detailed research on pregnancy outcomes following heat stress.
“If you remove pregnant women from the heat, you remove the health risk,” Kovats says. But that’s not always possible when women have to work outside to make a living. “It’s about inequality and women who don’t have access to cooling; it’s about pregnant women who have to work in the heat; it’s women who can’t fetch water except during the day due to the risk of violence.”
In Kilifi, Adelaide Lusambili, a medical anthropologist at Nairobi’s Africa International University, and her colleagues are working with the community to develop interventions for uplifting maternal health.11 These include addressing issues of water scarcity, raising awareness about staying hydrated and reducing workloads during pregnancy, constructing better ventilated homes and cooling spaces in healthcare facilities. Meanwhile, local tree plantation drives, to provide respite from scorching temperatures, are on the rise. For those to succeed, the challenge is picking the right species, planting them at appropriate densities, while avoiding areas with naturally low tree cover.12
In India, several cities and states have drafted heat action plans which involve providing heat advisories when temperatures exceed a certain threshold, creating public awareness about the health impact of heatwaves, and training medical staff to diagnose and treat heat-specific symptoms. “During summer months, we engage in social campaigns,” says Khyati Kakkad, a paediatrician at the LG Hospital in Ahmedabad, a city in western India that developed the county’s first heat action plan in 2013. “We talk to the public about the importance of staying hydrated, how to maintain a cool home environment, and discuss health hazards.” While there’s progress, there’s a lot more to done, she adds, especially to protect vulnerable groups such as pregnant women and infants during heatwaves.
On the other hand, “in places like the US, we’re very far behind,” Patel says. “We do need to get clinicians better equipped to know when these heat events are coming and to give patients appropriate counselling.” To prepare for high heat days, she suggests investing in preventative services such as mobile hydration vans and more cooling centres and improving access to these facilities.
The ultimate goal must still be to mitigate extreme heat fuelled by climate change, a global issue that affects us all. “We know heat is an environmental hazard, like air pollution, that needs to be managed,” Kovats says. A holistic and equitable approach, combining the reduction of greenhouse gas emissions with adapting our surroundings, is essential. Protecting health – particularly maternal health – against these climate-related changes requires global commitment alongside practical, localised action.
This article was commissioned as part of 'Our Planet Earth’. This is a digital initiative from BBC Earth, co-produced with Wellcome, bringing you compelling stories of our changing climate and its direct impacts on both wildlife and human health. Discover more here . #OurPlanetEarth.
Cover image: © Getty
1. Effects of climate change, 2. Food security, 3. Effects on human health, 4. Miriti Study, 5. Risk of Extreme heat on birth of newborns, 6. Heightened stillbirth risks, 7. Dehydration and heat strokes, 8. Reduction in blood flow to the placenta, 9. Preeclampsia, 10. Study from pregnant farm-working women in rural Gambia, 11. Interventions for uplifting maternal health, 12. Picking the right species 13. Heat action plans