A recent analysis found "suggestive evidence" that air pollution increases the risks of stillbirth, just as low income does, during the pregnancy's third trimester.
The study found there were about 2.6 million stillbirths in 2015, which happened during the 28th week or later. The wide differences in geographical prevalence suggested that these infant deaths could have been avoided.
In particular, a 4 microgram per cubic meter (µg/m3) exposure increase to small particulate matter of less than 2.5 micrometers in diameter (PM2.5) was linked to a 2 percent increased stillbirth risk.
Moreover, exposure to particles less than or equal to 10 micrometers in diameter (PM10), carbon monoxide, nitrogen dioxide and ozone also showed to be linked to increased stillbirth risks.
The research team reviewed past studies that looked into the link between stillbirths and air pollution up until 2015. The review found 13 studies eligible for the summary, but three studies from Asia and the United States were left out due to variations in pollutant types and study designs.
A related editorial from University of Copenhagen's Dr. Marie Pedersen highlighted that majority of the studies reviewed did not factor in other issues that could have contributed to the heightened risks of stillbirths. These factors included alcohol use, infections, obesity and work stress.
"If the evidence of an association between ambient air population and stillbirth is confirmed in future studies, it would be of major public health importance," said Pedersen.
She added that stillbirth is one of global health's "most neglected tragedies" in recent times, and that the mounting evidence showing the link between air pollution and stillbirths warrant further investigations.
"Further studies with better measures of air pollution, potential confounders and effect modifiers, are highly recommended to confirm or refute that exposure to ambient air pollution triggers stillbirth," added Pedersen.
According to the Lancet Stillbirth Series (2016), about 2.6 million stillbirths happen every year and 98 percent of these cases happen among low- and middle-income countries.
Moreover, 75 percent of the cases occur in South Asia and in sub-Saharan Africa. Putting it in perspective, in the United Kingdom alone, an estimated 10 babies are stillborn every single day.
The findings were published in the Occupational & Environmental Medicine journal on May 24.