High levels of air pollution seem to be linked to early miscarriages

By | October 15, 2019
A woman wearing a mask on a street in Causeway Bay as the roadside air monitoring station recorded an air pollution index of 141 at 12pm.

Exposure to air pollution may affect the development of a fetus

Edward Wong/South China Morning Post via Getty Images

High levels of air pollution may increase the chance of a missed miscarriage, according to data from pregnant women living and working in Beijing, China.

“We have clear evidence and accumulating knowledge that there is a true association [between air pollution and miscarriage],” says Tim Nawrot at Hasselt University in Belgium, who wasn’t involved in the study.

A missed or silent miscarriage is when a fetus dies or stops developing during pregnancy, usually without any symptoms. Such miscarriages tend to happen in the first trimester, and can be picked up on 12-week scans. Little is known about what causes them.

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Growing evidence suggests that exposure to air pollution could affect the development of a fetus. To find out if air pollution levels might be linked to missed miscarriages, Liqiang Zhang at Beijing Normal University and his colleagues assessed the health records of around 255,000 pregnant women in Beijing.

The team also collected data on the levels of four air pollutants recorded by air monitoring stations close to where each woman lived and worked. As well as tracking levels of tiny particles, such as soot, the researchers noted the amount of sulphur dioxide, ozone and carbon monoxide.

Just under 7 per cent of the women – about 17,500 individuals – experienced a missed miscarriage during their first trimester. Women who were older than 39 and those who worked as farmers or in blue-collar jobs seemed to be at greater risk.

The researchers found that those exposed to higher levels of air pollution had an increased risk of experiencing a missed miscarriage, although they didn’t directly test if pollution causes miscarriage. The finding builds on a recent study of women in the US, which also found a link between air pollution exposure and miscarriage risk.

Pollutants in the air seem to be able to infiltrate the placenta, according to recent work by Nawrot’s team. Once they reach the fetus, these chemicals might damage DNA. “They can interact with fetal development,” says Nawrot.

Zhang and his colleagues write that “pregnant women or those who want to become pregnant, must protect themselves from air pollution exposure not only for their own health but also for the health of their fetuses”. But Nawrot points out that “you can’t always avoid air pollution – everyone needs to breathe”.

Zhang’s team found that, since the Chinese government issued rules to reduce atmospheric pollution in 2013, air pollutant levels have declined, as has the risk of missed miscarriage. Governments ultimately have a responsibility to improve air quality, says Nawrot.

Journal reference: Nature Sustainability, DOI: 10.1038/s41893-019-0387-y

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