The impact of heat on pregnant women

There is ample evidence that heat is harmful to pregnant women and their unborn babies. What can be done to protect them?

Edrisa Sinjanka is passionate about his work as a midwife in Keneba, a rural village in Gambia, West Africa.

"I love my job very much, I like helping pregnant women during childbirth," he says.

But this is not always easy. Recently, women go to Sinjanka dehydrated, with dry lips and complaining of headaches. Pregnancy is tiring and some women are too weak to push through the labor process. He is also noticing other disturbing cases.

"Sometimes you have women who give birth to stillborn babies and you wonder: what's going on? Why are pregnant women having such problems?"

Sinjanka's opinion is that Gambia's high temperatures play a role in these tragedies. He has noticed that his patients, mostly field workers who spend hours every day under the scorching sun, have more severe symptoms of heat-related problems during pregnancy than those who work in offices, away from the sun.

It is concern that has prompted Sinjankan to join the local research project in 2019, as field coordinator in Keneba. Led by Ana Bonell, a clinical academic from the London School of Hygiene and Tropical Medicine (LSHTM) based in its Medical Research Unit in The Gambia, the project aimed to understand how high heat affects the physiology of pregnant laboring women as farmers and what impact this has on their unborn children.

"Farmers are often absent from studies of the impact of heat on the job, yet they provide food for millions. And with climate change, they are very vulnerable," says Bonelli.

For the study, 92 pregnant female farmers in and around Keneba were examined for signs of heat stress every two months as they continued their daily chores. What Bonelli discovered was significant: For every 1 degree Celsius increase in temperature, fetal stress—indicated by rapid heart rate and decreased placental blood flow—increased by 17 percent. A third of mothers have experienced such symptoms.

In The Gambia, where temperatures can reach up to 45 degrees Celsius and have risen 1 degree Celsius above average over the past sixty years, this poses a significant potential risk. Such extreme temperatures are occurring globally, with 2023 set to be the hottest year on record – although recent evidence suggests there is about a 95 per cent chance that 2024 will surpass it. High heat can endanger people's health, especially small children, the elderly and people with chronic health problems. But until recently one group has been overlooked: pregnant women.

During pregnancy, hormonal changes and increased skin surface area increase exposure to heat. In addition to discomfort, there is evidence that extreme heat can have harmful effects on both the mother and her unborn baby, ranging from hypertension to stillbirth.

Nearly a decade ago, publications first "suggested that pregnant women may be at risk during heat waves," says Kristie Eby, an epidemiologist at the University of Washington in Seattle who is studying the impact of climate change on human health for 25 years. "And recently there has been an acceleration in the study."

Still, the reality is that practical support for pregnant women facing extreme heat is still minimal today. Many nations, including the UK, do not specifically refer to pregnant women in their public heat guidelines. According to the American non-governmental organization Human Rights Watch, in August 2020, official heat safety websites from the US were more likely to mention pets in their instructions. The UN Population Fund – the UN's sexual and reproductive health agency – found in a report that only 20 percent of the 119 countries that have made climate change pledges mention maternal and fetal health in their plans. theirs.

As temperatures continue to rise, the question this raises is: how quickly can research translate into action to protect pregnant women and other vulnerable populations from extreme heat?

Multiple trials

Nathaniel DeNicola, an environmental health expert at the Johns Hopkins Health Institute in Washington, says the evidence is strong. Studies have linked increased heat exposure during pregnancy to a greater risk of hypertension and preeclampsia, a complication that can be fatal. Heat-affected pregnant women are also more likely to experience heart problems as their due date approaches and are more likely to develop gestational diabetes, which is diagnosed during pregnancy.

"There are many reasons to believe that the links we are seeing between extreme heat and outcomes are related. It's not a relationship per se, but there is a biological connection between them," says DeNicola.

DeNicola highlights the negative impacts of heat on birth outcomes. In a 2020 review of 68 studies done between 2007 and 2019, which together analyzed 32.7 million births in the US, DeNicola and co-authors found links between extreme heat and premature contractions, as well as preterm births.

Additionally, heat exposure has been linked to high rates of miscarriage and stillbirth. In a study that examined more than 140 stillbirths in the US, researchers found a 10 percent increase in the risk of stillbirth for every 1 degree Celsius increase in temperature above average.

"But the question is, what then?" says Skye Wheeler, senior researcher at Human Rights Watch. "We're looking at the science behind it, but that's not enough. What steps are we going to take about this?"

Combining research with action

That's the question of Gloria Maimelas, who leads the climate and health group at the HIV Institute for Reproductive Health at the University of the Witwatersrand in South Africa, where periods of extreme heat have been linked to increased mortality.

"We spent a lot of time describing the problem. Now we urgently need to move on to intervention studies", she says.

Maimela is currently leading two research projects in South Africa that are testing the success of several interventions to reduce heat risk in the lives of pregnant women. One she is excited about is based in the northern city of Tshwane: here, dozens of pregnant and post-pregnancy women will be fitted with cameras to record their experiences of heat. They will also be asked what they “think is reasonable in terms of messaging; what advice they would find acceptable to protect themselves and their unborn baby," she says.

This evidence will be incorporated into early heat wave warnings for pregnant women, which will also include guidance on how to cope with hot weather, Maimela explains. "We want to be able to say, please be aware that you are now exposed to extreme heat and that these are the steps you need to take to protect yourself," she says.

Although there's still a lot of room in what we know about the impact of heat on pregnancy, we can start taking steps using the evidence we already have, DeNicola says. "We know enough to consult, act and even provide some personal adaptations" - such as avoiding outdoor work during the hottest part of the day and hydration, he adds. "It's just a matter of getting that message across."

It is not always so easy in contexts like rural Kenya, where researchers are running a project under the LSHTM's Climate, Heat and Maternal and Postnatal Health in Africa (CHAMNHA) association, to overcome, among others, ingrained behaviors that increase women's exposure to heat.

In heat-affected Kilifi County, women do hard outdoor labor for a living, until it's time to give birth and immediately after giving birth, while wearing many clothes during pregnancy: “It's a cultural myth that if you show your pregnancy you will lose the child, so they try to hide it," says Adelaide Lusambili, a research scientist at the Aga Khan University in Nairobi. Here "the heat has normalized", she says. Coupled with rising temperatures, there is concern that this is a recipe for heat stress.

But in a pilot project launched in 2022, Lusambili and her colleagues have launched a public awareness program in clinics to educate expectant mothers about the dangers of heat and the steps they can take to keep themselves and their babies safe. them fresh during the heat. These have included limiting outdoor activities to the cooler hours of the day, wearing fewer layers, and boiling and drinking plenty of water. Researchers have also targeted other community members, hoping to elicit support from husbands and in-laws to help with household chores.

Towards practice and policy

Pregnant women are particularly at risk of extreme heat in parts of Africa, which have warmed faster than the global average over the past 60 years – a trend that is expected to continue.

However, even in affluent countries in temperate regions there are large disparities in vulnerability to heat, which are leaving some women at risk. That's why Wheeler believes policymakers need to look at the issue "through the lens of reproductive justice" — not just as a problem for all pregnant women, but especially for those who are poor and affected by racism.

To that end, Human Rights Watch is partnering with doulas, non-medical professionals who provide guidance, who will inform low-income pregnant women about how to protect themselves from the heat in Miami-Dade, Florida. "We're ground zero when it comes to climate change and these issues," says Esther McCant, a maternal care consultant and founder of Metro Mommy Agency, a doula service provider.

In Florida temperatures regularly reach 35 degrees Celsius and in homes without climate control this can be dangerous. "The families we serve often have trouble paying for additional maintenance on the air conditioning system, if they have it," says McCanti. Her company will integrate heat awareness into training that will include more than 90 doulas in Florida, Georgia and Hawaii in 2024 and beyond, which includes sharing practical information and support with clients.

That kind of financial and infrastructural support is important, Wheeler says. Some places are in the right direction, she adds, like India's Andhra Pradesh state, which gets very hot in the summer. Since 2019, it has offered heat guidance for pregnant women, hydration points on public transport, drinking water in public spaces and even compensation for heat-related deaths.

Meanwhile, Bonelli and Maimela are involved in research that may prompt policymakers to take similar practical steps. In a new multi-year project based in the Pakistani cities of Karachi and Matiar, Bonelli is working with urban planners and architects to design community cooling points and naturally ventilated housing to ease the heat burden on expectant mothers. Maimela is investigating the role that cash subsidies to poor families can play in supporting pregnant women to adapt to the heat.

For her part, Bonelli is continuing to gather evidence on how extreme heat is affecting pregnant women and their unborn babies. She will then work with more than 700 pregnant women from The Gambia to investigate whether there are epigenetic changes to changing temperatures during the different trimesters of pregnancy. She and her team will also take samples of the placenta and conduct behavioral tests of neurons in the newborns to further study the harmful and potential effects of heat on fetal development and the lives of newborns. .

As this evidence accumulates, Sinjanka does her best to ensure the women of Keneba have a comfortable and supportive birth. "I always want to see them smiling at the end of the trip," he says. Ultimately, he believes it is research, coupled with action, that will do this for his patients.