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Air pollution and stillbirths are linked, study finds

Air pollution and stillbirths are linked, study finds

Aapproximately 140 million babies were born in the world last year-the equivalent of add a whole new Russia to the world population. Not among these typically blessed events are the number of families whose pregnancies end tragically. According to United Nations Interagency Group for Child Mortality Estimation, approximately 2 million pregnancies worldwide end in stillbirth each year. The causes of natal death are many – from fetal abnormalities and labor complications to maternal hypertension, infections and placental malformations.

Now, according to a new study in Nature Communication, there is another, particularly pernicious cause that can account for up to 39.7% of stillbirths in low- and middle-income countries: air pollution, particularly in the form of fine particles measuring 2.5 microns – or millionths of a meter – or less. The particles, about 3% the width of a human hair, typically come from vehicle exhaust, burning coal and fuel oil, and natural sources like wildfires.

According to the new research, led by environmental scientist and public health specialist Tao Xue at Peking University Health Science Center in Beijing, every 10 micrograms – or millionths of a gram – of so-called PM2.5 particles per cubic meter of air increases the risk of stillbirth by 11%, with the consequences being greater for older mothers than for younger ones.

“The United Nations calls the global burden of stillbirths a neglected tragedy,” write the authors of the article. “The prevention of stillbirths depends on a comprehensive understanding of the underlying risk factors.”

The World Health Organization (WHO) has set a so-called reference level – or maximum safe exposure – of PM2.5 at 5 micrograms per cubic meter of air. Above this level, particles can contribute to heart disease, asthma, decreased lung function and premature death in people with pre-existing heart or lung disease. Researchers have long established a potential link between PM2.5 exposure and stillbirth, but what they hadn’t, until Tao and his colleagues broached the subject, was to study how the burden falls disproportionately on people in the poorest countries.

According to the World Bank, the global average concentration of PM2.5 is an alarming 46 micrograms per cubic meter, nine times the WHO reference level. But the burden is not distributed equitably. In Australia, it is 9 micrograms more tolerable; in Canada, there are only six. The Bahamas clock in at just 5.58. It is elsewhere, in the less developed world, that the pollution problem hits hardest.

To conduct their study, the investigators selected 137 low- and middle-income countries in which data from the Ministry of Health surveys (DHS), a division of the United States Agency for International Development (USAID), are home to 98% of the global incidence of stillbirths. They cross-referenced these mortality figures with other WHO data Air Quality Guidelines detailing the severity of PM2.5 pollution in each of these countries. The results drew a clear line between particulate emissions and the incidence of stillbirths.

India, the hardest hit country, with an annual average of 217,000 stillbirths (out of 25 million live births), had a PM2.5 concentration of 60.15 micrograms per cubic meter of air, or 12 times the WHO reference level. Pakistan, the second most affected country, with 110,000 stillbirths per year (compared to 6.075 million live births), weighed 63.16 micrograms of pollution. Next come Nigeria (93,000 stillbirths, 7.8 million live births and 69.66 micrograms); China (64,000 stillbirths, 10.6 million live births and 51.11 micrograms) and Bangladesh (49,000 stillbirths, 2.8 million live births and 69.58 micrograms). In addition to PM2.5 air pollution, the study also cites the possibility of high natural concentrations of dust, particularly in sub-Saharan Africa and the Arabian Desert region, as another source of hazardous particles. .

Maternal age played an important role in mortality risk. Drawing on DHS data, as well as two existing meta-analyses of stillbirth incidence, the researchers calculated that mothers who lost their children at birth were, on average, 3.81 years old. more than those whose babies were born successfully. The greatest risk of stillbirth in high PM2.5 countries was for mothers aged 34 or older.

The mechanism that links PM2.5 concentration to stillbirth is uncertain. “Although the potential biological mechanisms for the association of PM2.5 exposure and pregnancy loss are still unclear,” the researchers wrote, “certain pathways may explain it to some extent.” The researchers suggest three possibilities.

First, when a pregnant person inhales PM2.5 particles, they enter the bloodstream and can directly cross the placental barrier where they flow into the fetus, causing low oxygen levels or immune problems in the fetus. baby, both of which can be associated with fetal disorders. death. It is also possible that exposure to PM2.5 could lead to the development of methemoglobin in the parent, a form of hemoglobin that does not bind oxygen and therefore does not provide enough oxygen to the fetus, also leading to immune problems. and potentially death in the womb. Finally, PM2.5 can lead to abnormalities or malformations of the placenta itself, preventing it from supporting a fetus throughout pregnancy.

The outlook was not entirely bleak. The study notes that the global stillbirth rate actually decreased by 1.95% from 2000 to 2009 and then by 2.05% from 2009 to 2019. It attributes the trend to improving air quality in several countries, notably China, which is slowly receding. coal-fired power plants and clean their power grid with renewable energy sources.

In the meantime, pregnant women can take steps to reduce their exposure to PM2.5 pollution and better monitor the potential impact of the particles. Wearing N95 or KN95 masks outside on high pollution days, avoiding the outdoors when the air quality is worst, and installing air purifiers at home can all help. The same applies to improving prenatal care and prompt intervention, including caesarean sections, in the event of premature or complicated labour.

Pregnancy and childbirth have never been easy. But more often than they do now, they should end up with a happy outcome. In at least 137 countries, our own mismanagement of the health of the planet too often robs families of that joy.

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Write to Jeffrey Kluger at jeffrey.kluger@time.com.

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