Researchers estimated that for every increase of five micrograms per cubic metre in exposure to fine particulate matter during pregnancy, the risk of low birthweight at term rose by 18 per cent. Photo: Danny Lawson/PA Wire

Pregnant women who are exposed to even low levels of air pollution are at an increased risk of giving birth at term to low-birthweight babies, according to a large-scale study.

Air pollutants – in particular, fine particulates found in traffic fumes and industrial air pollutants – along with traffic density increased the risk of low birthweight and reduced average head circumference of babies born at term, research has shown.

The study, drawn from data on 74,000 pregnant women in 12 European countries gathered between 1994 and 2011 and published in the Lancet Respiratory Medicine, estimated concentrations in the air of nitrogen oxides and fine particulates at home addresses.

Traffic density on the nearest road and total traffic load on all major roads within 100 metres of the residence was also recorded.

Researchers estimated that for every increase of five micrograms per cubic metre in exposure to fine particulate matter – emitted by sources including diesel engines and coal-fired power stations – during pregnancy, the risk of low birthweight at term rose by 18 per cent.

This increased risk remained at levels below the existing EU annual air quality limit of 25 micrograms per cubic metre.

The widespread exposure of pregnant women worldwide to urban ambient air pollution provides a clear message to policymakers to improve the quality of the air we all share

The average exposure to fine particulate matter during pregnancy in those studied ranged from less than 10 micrograms to nearly 30 micrograms per cubic metre.

The study authors estimated that if levels of fine particulates were reduced to 10 micrograms per cubic metre – the World Health Organisation annual average air quality guideline value – 22 per cent of cases of low birthweight among term deliveries could be prevented.

Low birthweight for a baby born at term was classified as less than 2.5kg. The study took into account other factors such as maternal smoking, age, weight and education.

Lead author Marie Pedersen, from the Centre for Research in Environmental Epidemiology in Barcelona, said: “Our findings suggest that a substantial proportion of cases of low birthweight at term could be prevented in Europe if urban air pollution, particularly fine particulate matter, was reduced.

“The widespread exposure of pregnant women worldwide to urban ambient air pollution at similar or even higher concentrations than those assessed in our study provides a clear message to policymakers to improve the quality of the air we all share.”

The findings are the latest in a long series of studies documenting the negative effects of traffic pollution on health and well-being.

Low-level exposure to traffic fumes can increase the risk of lung cancer and exposure to traffic fumes and industrial pollution can dramatically increase a mother’s chances of having a child with autism.

Defective kidneys may be a sign that traffic pollution is harming the arteries and traffic fumes may also increase the risk of stroke by narrowing the arteries that carry blood to the brain, research has suggested.

Traffic pollution has also been found in research to cause as much childhood asthma as passive smoking.