Scientists found women exposed to higher nitrogen dioxide levels had a 16% greater risk of miscarriage.

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Pregnant women are at an increased risk of miscarrying if they are exposed to elevated levels of a type of air pollution, a study suggests.

Researchers in the US found a 16% increase in the risk of miscarriage among women exposed to higher levels of nitrogen dioxide, a gas created by petrol and diesel vehicles.

The findings were described as “upsetting” by one of the doctors who led the study at the University of Utah.

The warning comes amid heightened concern over air pollution’s potential links to a growing list of diseases and conditions including stroke, dementia and autism.

The NHS says that, among women who know they are pregnant, an estimated one in eight pregnancies ends in miscarriage, while many more occur before a woman is aware she has become pregnant.

The research into potential links with pollution saw doctors analyse the records of more than 1,300 women who sought help at the University of Utah’s emergency department following miscarriage between 2007 to 2015.

The team calculated the risk of miscarriage during periods of three or seven days after a spike in levels of common air pollutants including small particulate matter and nitrogen dioxide.

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They found an increased risk in miscarriage for women exposed to elevated levels of nitrogen dioxide, which equalled a rise of 16% for a 10 parts per billion increase during a seven-day window.

The particulate matter did not significantly associate with an increased risk of miscarriage.

Matthew Fuller, associate professor of surgery at the university, said: “The results of this study are upsetting, and we need to work together as a society to find constructive solutions.”

Dr Fuller said pregnant women should raise any health concerns they may have with their doctor.

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They can also manage the risk by avoiding outdoor physical activity on poor air quality days.

Research analyst Claire Leiser, who worked with Dr Fuller on the study, noted that the data only related to the most severe cases during a small window of time.

The records did not account for women who may have sought outpatient care through their obstetric or primary care providers.