Exposure to common air pollutants and traffic during pregnancy significantly increases the risk of restricted fetal growth, even at levels well below the limits stipulated in current European Union (EU) air-quality directives, according to one of the largest studies of its kind, published in The Lancet Respiratory Medicine.

The study assessed the impact on birthweight of fine particulate matter (PM 2.5; diameter less than 2.5 microm), found, for example, in traffic fumes and industrial air pollutants. The researchers estimate that for every increase of 5 microg/m³ in exposure to PM 2.5 during pregnancy, the risk of low birthweight at term rises by 18%. Importantly, this increased risk was also detected at levels below the existing EU annual air quality limit of 25 microg/m³.

"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", explains lead author Dr Marie Pedersen from the Centre for Research in Environmental Epidemiology (CREAL), an ISGlobal alliance research centre.

ESCAPE Study

Pedersen was part of a team of European researchers coordinated by CREAL (Barcelona) and INSERM (Grenoble) that studied the association between exposure to low levels of air pollution during pregnancy and low birthweight at term (less than 2500 g after 37 weeks of gestation). Low birthweight has been linked to respiratory problems in childhood and other diseases later in life. The impact on head circumference was also studied because of the potential effect on neurodevelopment.

Using data from the European Study of Cohorts for Air Pollution Effects (ESCAPE, coordinated by the University of Utrecht, the Netherlands), the investigators pooled data from 14 cohort studies in 12 European countries involving over 74 000 women who had singleton births between February 1994 and June 2011.

Air pollution concentrations of nitrogen oxides and particulate matter were estimated at the mothers' homes using land-use regression models. Traffic density on the nearest road and total traffic load on all major roads within 100 m of the residence were also recorded.

All air pollutants, particularly PM 2.5, and traffic density increased the risk of low birthweight at term and reduced average head circumference at birth, after accounting for other factors such as maternal smoking, age, weight, and education.

Average exposure levels of PM 2.5 during pregnancy in the study population ranged from less than 10 microg/m³ to nearly 30 microg/m³. The researchers estimated that if levels of PM 2.5 were reduced to 10 microg/m³ (the WHO annual average air quality guideline value), 22% of cases of low birthweight among term deliveries could be prevented.

According to Dr Pedersen, "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 policy makers to improve the quality of the air we all share."

More information

Pedersen M. et al. Ambient air pollution and low birthweight: a European cohort study (ESCAPE). The Lancet Respiratory Medicine - 15 October 2013. DOI: 10.1016/S2213-2600(13)70192-9