Traffic-related air pollution, preterm birth and term birth weight in the PIAMA birth cohort study
Introduction
There is growing evidence for adverse effects of maternal exposure to ambient air pollution during pregnancy on pregnancy outcomes including fetal growth and preterm delivery. A number of recent reviews (Glinianaia et al., 2004, Lacasana et al., 2005, Maisonet et al., 2004, Sram et al., 2005, Stillerman et al., 2008) summarize the epidemiological evidence. The effects of different air pollutants including particulate matter (PM), nitrogen dioxide (NO2), carbon monoxide (CO), and sulphur dioxide (SO2) on pregnancy outcomes have been studied. The authors conclude that, although results are not always consistent, the data suggest that adverse effects of air pollution on fetal growth and preterm delivery may occur and recommend additional research on this topic. Evidence was judged to be stronger for low birth weight than for premature birth in one review (Sram et al., 2005). Other reviews, however, indicated the opposite (Maisonet et al., 2004) or were less conclusive (Glinianaia et al., 2004, Lacasana et al., 2005). Although the effects, if any, are probably small, the public health impact may be considerable due to the widespread nature of the exposure and the long-term health impacts of low birth weight and preterm birth (Osmond and Barker, 2000). The mechanisms behind the associations between exposure to ambient air pollution and pregnancy outcomes are not clear yet. Kannan et al. (2006) describe potential biologic pathways including systemic oxidative stress and inflammation, changes in blood coagulation, endothelial function, and hemodynamic responses. Likewise, the crucial window(s) of exposure are not clear, yet. For low birth weight and preterm birth, the first trimester exposures and the exposures during the third trimester and during the last weeks preceding birth have been implicated as having most relevance (Ritz and Wilhelm, 2008).
Most of the studies performed so far made use of data from birth registers that have been routinely collected and where information on important confounding variables such as maternal smoking during pregnancy is usually either very limited on the individual level or lacking completely. Relying on data from existing birth or pregnancy cohort studies rather than birth registers has the advantage that usually large amounts of individual data are available. Another deficiency of most of the studies that have been done so far involves the assessment of exposure. Individual exposure measurements are not feasible in large study populations. Therefore, exposure was usually estimated using data from a limited number of routine air quality monitoring sites in the study area, which may be located several kilometers from the homes of study subjects. This may lead to considerable measurement error, especially in relation to pollution from local sources such as traffic (Cyrys et al., 1998, Fischer et al., 2000, Lebret et al., 2000). To overcome this problem, Slama et al. (2007) introduced the use of more sophisticated spatio-temporal exposure models using Geographic Information Systems (GIS), measurement data, and stochastic modeling. We adopted this approach and estimated individual exposures during the entire pregnancy, 1st trimester, and the last month of pregnancy in the present study.
The objective of the present study is to explore the effect of exposure to traffic-related air pollution during the entire pregnancy, 1st trimester, and the last month of pregnancy on preterm birth and fetal growth in a birth cohort study of almost 3900 children living in the Netherlands with individual information on maternal physical, lifestyle, and socio-demographic characteristics.
Section snippets
Study population
The Prevention and Incidence of Asthma and Mite Allergy (PIAMA) study is a prospective birth cohort study (Brunekreef et al., 2002). Women were recruited in 1996–1997 during their second trimester of pregnancy from a series of communities in the North, West, and Centre of The Netherlands. Non-allergic pregnant women were invited to participate in a “natural history” study arm. Pregnant women identified as allergic through a screening questionnaire were primarily allocated to an intervention arm
General characteristics and pregnancy outcomes
Exposures were successfully estimated for 3853 of the 3863 children (99.7%). Distributions of pregnancy outcomes and covariates for all children are presented in Table 1. Distributions of pregnancy outcomes and most covariates differed between the three study regions (Table 1 of the online supplement). Associations between pregnancy outcomes and covariates are presented in Table 2.
Exposure to air pollution
The range in levels was larger for NO2 and soot than for PM2.5 (Table 3). Correlations between the different
Discussion
Our findings provide little support to the hypothesis of an adverse effect of maternal exposure to air pollution during pregnancy on term birth weight. Exposure to soot during entire pregnancy and during the last month of pregnancy tended to be associated with a small, statistically non-significant increase in risk of preterm delivery.
A number of studies mainly performed in North America and Australia have reported associations between NO2 and PM2.5 exposure during pregnancy and preterm birth.
Conclusions
This study provides little evidence for an adverse effect of maternal exposure to traffic-related air pollution during pregnancy on term birth weight. There was a tendency towards an increased risk of preterm birth with increasing air pollution exposure, but statistical power was low.
Review and approval
The Institutional Review Boards of the participating institutes approved the study protocol, and written informed consent was obtained from all participants.
Funding
The PIAMA study is supported by The Netherlands Organization for Health Research and Development; The Netherlands Organization for Scientific Research; The Netherlands Asthma Fund; The Netherlands Ministry of Spatial Planning, Housing, and the Environment; and The Netherlands Ministry of Health, Welfare, and Sport. Ulrike Gehring was supported by a research fellowship of the Netherlands Organization for Scientific Research (NWO).
References (44)
- et al.
Residential mobility during pregnancy and the potential for ambient air pollution exposure misclassification
Environ. Res.
(2010) - et al.
Traffic-related differences in outdoor and indoor concentrations of particles and volatile organic compounds in Amsterdam
Atmos. Environ.
(2000) - et al.
Low levels of ambient air pollution during pregnancy and fetal growth among term neonates in Brisbane, Australia
Environ. Res.
(2007) - et al.
Small area variations in ambient NO2 concentrations in four European areas
Atmos. Environ.
(2000) - et al.
A review of the literature on the effects of ambient air pollution on fetal growth
Environ. Res.
(2004) - et al.
Methodological issues in studies of air pollution and reproductive health
Environ. Res.
(2009) - et al.
Association between GIS-based exposure to urban air pollution during pregnancy and birth weight in the INMA Sabadell Cohort
Environ. Health Perspect.
(2009) - et al.
Effect of maternal asthma and gestational asthma therapy on fetal growth
J. Asthma
(2007) - et al.
Ambient air pollution and low birth weight in Connecticut and Massachusetts
Environ. Health Perspect.
(2007) - et al.
Estimating long-term average particulate air pollution concentrations: application of traffic indicators and Geographic Information Systems
Epidemiology
(2003)