Articles
Ambient air pollution and low birthweight: a European cohort study (ESCAPE)

https://doi.org/10.1016/S2213-2600(13)70192-9Get rights and content

Summary

Background

Ambient air pollution has been associated with restricted fetal growth, which is linked with adverse respiratory health in childhood. We assessed the effect of maternal exposure to low concentrations of ambient air pollution on birthweight.

Methods

We pooled data from 14 population-based mother–child cohort studies in 12 European countries. Overall, the study population included 74 178 women who had singleton deliveries between Feb 11, 1994, and June 2, 2011, and for whom information about infant birthweight, gestational age, and sex was available. The primary outcome of interest was low birthweight at term (weight <2500 g at birth after 37 weeks of gestation). Mean concentrations of particulate matter with an aerodynamic diameter of less than 2·5 μm (PM2·5), less than 10 μm (PM10), and between 2·5 μm and 10 μm during pregnancy were estimated at maternal home addresses with temporally adjusted land-use regression models, as was PM2·5 absorbance and concentrations of nitrogen dioxide (NO2) and nitrogen oxides. We also investigated traffic density on the nearest road and total traffic load. We calculated pooled effect estimates with random-effects models.

Findings

A 5 μg/m3 increase in concentration of PM2·5 during pregnancy was associated with an increased risk of low birthweight at term (adjusted odds ratio [OR] 1·18, 95% CI 1·06–1·33). An increased risk was also recorded for pregnancy concentrations lower than the present European Union annual PM2·5 limit of 25 μg/m3 (OR for 5 μg/m3 increase in participants exposed to concentrations of less than 20 μg/m3 1·41, 95% CI 1·20–1·65). PM10 (OR for 10 μg/m3 increase 1·16, 95% CI 1·00–1·35), NO2 (OR for 10 μg/m3 increase 1·09, 1·00–1·19), and traffic density on nearest street (OR for increase of 5000 vehicles per day 1·06, 1·01–1·11) were also associated with increased risk of low birthweight at term. The population attributable risk estimated for a reduction in PM2·5 concentration to 10 μg/m3 during pregnancy corresponded to a decrease of 22% (95% CI 8–33%) in cases of low birthweight at term.

Interpretation

Exposure to ambient air pollutants and traffic during pregnancy is associated with restricted fetal growth. A substantial proportion of cases of low birthweight at term could be prevented in Europe if urban air pollution was reduced.

Funding

The European Union.

Introduction

Air pollution with ambient particulate matter is one of the most important controllable health threats.1 Maternal exposure to air pollution during pregnancy could increase the risk of preterm birth (<37 weeks of gestation), low birthweight (<2500 g), congenital malformations, and other adverse health effects.2, 3, 4, 5, 6, 7, 8

Infants with low birthweight are at greater risk of mortality and morbidity than are infants with higher birthweight.9, 10, 11 Low birthweight has been associated with wheezing and asthma in childhood,12 and with decreased lung function in adults,13 although findings are not consistent. Infants with low birthweight could have accelerated weight gain in the first 3 months of infancy, which has been associated with asthma symptoms in children aged up to 4 years.14 In addition to active and passive smoking,15 atmospheric pollution exposure is a highly prevalent and controllable potential risk factor for low birthweight.2, 3, 4, 5, 6, 7, 8

Meta-analyses3, 4, 5 have shown heterogeneity of effects of air pollution across studies, but have suggested that particulate matter with an aerodynamic diameter of less than 2·5 μm (PM2·5) is most consistently associated with low birthweight. Exposure assessment in many previous studies of the effects of air pollution on fetal growth relied on routine air pollution monitoring stations, which do not capture within-city exposure contrasts adequately, possibly resulting in misclassification of exposure and possibly reduced risk estimates.2, 3, 4, 5, 6, 7, 8, 16 In studies in the past 7 years, methods such as land-use regression (LUR) have been applied to improve spatial resolution.2, 3, 4, 5, 6, 7, 8, 16, 17, 18 The largest body of evidence comes from a series of studies in the Los Angeles basin (CA, USA), where air pollution sources and mixtures could be different from those in smaller urban areas.3, 4, 5, 6, 7, 8 Apart from a few studies (usually based on birth registers17, 18), many had small sample sizes or poor control of confounders.2, 3, 4, 5, 6, 7, 8, 16 The individual excess risk of low birthweight reported in these studies was low, but the large proportion of exposed women in the general population warrants an estimation of the attributable risk at the population level.

In this study, we investigated the associations of low levels of exposure to air pollutants with low birthweight at term, birthweight, and head circumference in a population from urban areas. We postulated that increased maternal exposure to ambient air pollution during pregnancy would be associated with intrauterine growth restriction. Additionally, we estimated the proportion of cases of low birthweight at term that were attributable to air pollution.

Section snippets

Study population

This study was part of the European Study of Cohorts for Air Pollution Effects (ESCAPE), in which the association between exposure to outdoor air pollution and health is being investigated with prospective cohort studies.19 We pooled data from 14 European mother–child cohort studies in which birthweight was not part of inclusion criteria: MoBa (Norway); BAMSE (four centres; Sweden); DNBC (Denmark); KANC (Lithuania); BiB (England); ABCD, GENERATION R, and PIAMA (three centres; Netherlands);

Results

Mothers were predominately born in the country of their cohort, were non-smokers, and had a mean age of 30 years (table 1, appendix p 8). About 85% of women for whom information about change of address was available did not change address during pregnancy (table 1). Mean gestational age was almost 40 weeks (table 1). 3627 (4·9%) of the 74 178 births were preterm. 3087 infants (4·2%) had low birthweight.

PM2·5 and PM10 concentrations were lower in northern areas than in central and southern areas

Discussion

We have shown that ambient air pollutants—particularly PM2·5—and traffic density are associated with increases in risk of low birthweight at term and reductions in birthweight and birth head circumference (panel). Our findings suggest that in-utero exposure to ambient air pollution in European urban areas could explain a substantial proportion of cases of low birthweight at term. We used data from a large population with fairly low exposure levels, and increased risks were recorded in the

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