Nearly one million stillbirths a year can be attributed to air pollution, according to the first global study.
Research has estimated that nearly half of stillbirths could be linked to exposure to pollution particles smaller than 2.5 microns (PM2.5), mostly produced by burning fossil fuels.
The study looked at 137 countries in Asia, Africa and Latin America, where 98% of stillbirths occur. Dirty air was previously known to increase the risk of stillbirth, but the research is the first to assess the number of fetal deaths. The work was based on data from more than 45,000 stillbirths and live births.
Stillbirths were described as a “neglected tragedy” in a 2020 report published by Unicef. The heavy impact of stillbirths on mothers and their families would mean that measures to prevent them would improve women’s health and equality, say the scientists behind the new work.
The epidemiological study did not examine how small particle pollution could cause stillbirths. But that followed the revelation in October that toxic air pollution particles had been found in the lungs and brains of fetuses. Air pollution particles were first detected in placentas in 2018 and at that time dirty air was known to be strongly correlated with increased miscarriages, premature births, insufficient birth weight and impaired brain development.
“Achieving World Health Organization (WHO) air quality targets could prevent a considerable number of stillbirths,” said the scientists, led by Dr Tao Xue of Peking University in China. “Current efforts to prevent stillbirth focus on improving medical services, but compared to clinical risk factors, environmental factors are usually invisible.”
The scientists added: “Air quality policies, which have been adopted in some countries, such as China, can prevent stillbirths. In addition, personal protections against air pollution, i.e. wearing masks, installing air purifiers, avoiding going out in the event of air pollution , may also protect vulnerable pregnant women.
The research, published in Nature Communications, used data on stillbirths and air pollution between 1998 and 2016 in 54 low- and middle-income countries (LMICs), including Pakistan, India and Nigeria. This was used to estimate the number of stillbirths attributable to PM2.5 exposure in the 137 low- and middle-income countries, taking into account that the impact of polluted air was greater on older mothers. elderly.
Virtually all mothers in the study were exposed to PM2.5 levels above the current WHO reference level of 5 micrograms per cubic meter (μg/m3). There were 2.09 million stillbirths recorded in the countries studied in 2015, and 950,000 of these (45%) were attributable to exposure above 5 μg/m3, the study estimates.
The WHO guideline for PM2.5 was 10 μg/m3 until 2021 and 99% of mothers in the study were exposed to higher levels of polluted air. This was linked to 830,000 stillbirths, or 40% of the total, according to the study. The proportion of stillbirths attributed to PM2.5 pollution was particularly high in Pakistan, India, Nigeria and China. Overall, the researchers found that an increase in PM2.5 exposure of around 10 µg/m3 was associated with an 11% increased risk of stillbirth.
The total number of stillbirths rose from 2.31 million in 2010 to 1.93 million in 2019. Researchers said reduced air pollution in some countries, such as China, may be a significant reason for the this fall. They estimated that reducing air pollution to the level of 10 ug/m3 today could prevent 710,000 stillbirths per year. “Due to universal exposure to air pollution, it is one of the largest contributors to global stillbirths,” Xue said.
How air pollution can cause stillbirths is still unclear. But the researchers said pollution particles crossing the placenta could cause “irreversible embryonic damage” and could also damage the placenta itself. Air pollution could also limit the ability of the mother’s body to transmit oxygen to the fetus.
The scientists said that while the global number of stillbirths was falling, there was no decline in around half of the low- and middle-income countries assessed. They noted that the rate of decline in stillbirths was slower than the decline in under-five mortality. “This suggests that efforts to promote maternal health are patchy across different adverse outcomes, and that interventions for stillbirths are inadequate,” they said.
Professor Gregory Wellenius, director of the Center for Climate and Health at Boston University in the US, who was not involved in the research, said: ‘This study is new and demonstrates that at current levels, the air pollution contributes to a significant number of stillbirths. around the world.
“Health impact assessments like this are always based on a number of important assumptions. Although the fraction of stillbirths that could be prevented with significant reductions in PM2.5 is uncertain, the study adds to the wealth of scientific evidence showing that reducing air pollution levels will improve health. people around the world, especially among the most vulnerable. .”
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