The findings suggest exposure to air pollution from traffic in London during pregnancy is associated with an increased risk of low birth weight.
The researchers, who say their findings are applicable to other UK and European cities, are calling for environmental health policies to improve air quality in urban areas.
“This new research is worrying for pregnant women who live in cities and it’s high time we had stronger health policies to improve urban air quality,” said
Elizabeth Duff, senior policy adviser, at the National Childbirth Trust (NCT) told HuffPost UK.
“In the meantime, mums-to-be can keep an eye on air pollution in their area online and might want to avoid particularly toxic areas by steering clear of busy roads and taking back streets instead.
“They may also want to check for high pollution levels and consider reducing outdoor activities on these days.”
For the study, a team of London-based researchers led by Imperial College London set out to investigate the relation between exposure to air and noise pollution from road traffic during pregnancy and two birth weight outcomes - low birth weight (less than 2500g) and being born small for gestational age.
Using national birth registers, they looked at more than 540,000 full-term births in Greater London between 2006 and 2010.
The mother’s home address at time of birth was recorded and the average monthly concentrations of traffic-related pollutants and road traffic noise levels were estimated.
The researchers found that increases in traffic-related air pollutants - especially PM2.5 [harmful levels of fine particles] - were associated with a 2% to 6% increased odds of low birth weight and 1% to 3% increased odds of being small for gestational age.
There was no evidence that increasing road traffic noise exposure was independently associated with birth weight but the authors say they “cannot rule out that an association might be observed in a study area with a wider range of noise exposures.”
“Our findings suggest that air pollution from road traffic in London is adversely affecting foetal growth,” the authors said.
The authors estimated that reducing London’s annual average PM2.5 concentration by 10% would prevent approximately 90 babies (3%) being born at term with low birth weight each year in London.
“With the annual number of births projected to continue increasing in London, the absolute health burden will increase at the population level, unless air quality in London improves,” they concluded.
How to find out the current level of air pollution in your area:
You can find out the current level of air pollution in your region by heading to the Defra website. You can click a coloured area on the map to view information. The results are based on the maximum air quality index measured across all stations in each region.
The colour code highlights whether the level is “low”, up to “very high”. Click here to find out what the pollution level is where you live.
Or to get up-to-date alerts, follow the daily forecast tweets on Twitter.
Dr Sotiris Vardoulakis, head of Public Health England’s environmental change department, previously told HuffPost UK: “Anyone experiencing discomfort such as sore eyes, cough or sore throat should consider reducing activity, particularly outdoors.”