Exposure to air pollution may increase the risk of stillbirth, new research suggests.
Stillbirths, which are classed as such if a baby is born dead after at least 24 weeks of pregnancy, occur in one in every 200 births.
Researchers have called for tighter curbs on car exhausts and industrial waste emissions to reduce the risk of air pollutants after their research concluded that exposure to ambient air pollution heightens the risk of stillbirth.
Following a systematic review of 13 studies on the subject, published in the journal Occupational & Environmental Medicine, the researchers found the risk was particularly heightened during the third trimester of pregnancy.
"Our results provide suggestive evidence that ambient air pollution is a risk factor for stillbirth," they wrote.
"Pregnant women should be aware of the potential adverse effects of ambient air pollution, although the prevention against exposure to air pollutants generally requires more action by the Government than by the individual."
They added: "Policies such as control of vehicular emissions, fuel quality improvement and control of industrial waste emissions should be developed and implemented to reduce the risk of air pollutants."
The air pollutants linked to a heightened risk included: small particulate matter of less than 2.5 microns in diameter (PM2.5), PM10, nitrogen dioxide, sulphur dioxide, carbon monoxide and ozone.
But they stressed that further research is needed to strengthen the evidence.
In a linked editorial, Dr Marie Pedersen, of the Centre for Epidemiology and Screening at the University of Copenhagen, Denmark, wrote: "Stillbirth is one of the most neglected tragedies in global health today, and the existing evidence deserves additional investigation.
"If the evidence of an association between ambient air pollution and stillbirth is confirmed in future studies, it would be of major public health importance.
"Although the reported summary effect estimates were relatively small, the ubiquitous nature of ambient air pollution exposure suggests that exposure to ambient air pollution may have a large population-attributable risk for stillbirth."