Almost a million stillbirths a year can be attributed to air pollution, according to the first global study.

The research estimated that almost half of stillbirths could be linked to exposure to pollution particles smaller than 2.5 microns (PM2.5), mostly produced from the burning of fossil fuels.

The study covered 137 countries in Asia, Africa and Latin America, where 98% of stillbirths occur. Dirty air was already known to increase the risk of stillbirth but the research is the first to assess the number of foetal 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 action to prevent them would boost women’s health and equality, the scientists behind the new work said.

The epidemiological study did not examine how small particle pollution could cause stillbirths. But it followed the revelation in October that toxic air pollution particles were found in the lungs and brains of foetuses. Air pollution particles were first detected in placentas in 2018 and by then dirty air was known to strongly correlate with increased miscarriages, premature births, low birth weights and disturbed brain development.