Academic journal article Scandinavian Journal of Work, Environment & Health

Air Pollution Exposure and Adverse Pregnancy Outcomes in a Large UK Birth Cohort: Use of a Novel Spatio-Temporal Modelling Technique

Academic journal article Scandinavian Journal of Work, Environment & Health

Air Pollution Exposure and Adverse Pregnancy Outcomes in a Large UK Birth Cohort: Use of a Novel Spatio-Temporal Modelling Technique

Article excerpt

Pregnancy outcome is determined by the ability of the fetus to thrive, which depends on a complex combination of genetic, social, and environmental factors (1). If, during pregnancy, a mother is exposed to increased environmental or social stressors, this could result in an increased risk of restricted growth of the fetus or a preterm birth (PTB). These adverse perinatal outcomes are strong predictors for infant mortality and morbidity (2). Moreover, epidemiological evidence has suggested the long-term implications of a sub-optimal in utero environment with links to an increased risk for health conditions in later life, such as cardiovascular disease and type 2 diabetes (3, 4).

A range of environmental exposures during pregnancy have been investigated to understand better the contribution of environmental factors on the vulnerable fetus, including water contamination (5), electromagnetic fields (6) and pesticides (7). A large body of work now exists from around the world investigating the effects of air pollution on pregnancy and the subsequent birth outcomes, which have given rise to several recent reviews (8-10). Numerous studies have found evidence to support the hypothesis that air pollution can increase the risks of PTB (11-13) and impaired fetal growth (14-16); however, the results are not yet consistent enough to confirm a causal link with specific pollutants.

Limitations of previous studies mostly relate to exposure assessment methods that may not adequately capture spatial and temporal pollution variation, small sample sizes, and appropriateness of confounder adjustments (17). Most studies investigating the association between air pollution and adverse pregnancy outcomes use a retrospective cohort study design in order to be better able to achieve the necessary power to detect relatively small effects. A retrospective design presents the challenge of assigning pollution estimates that best represent the spatial and temporal heterogeneity of multipollutant exposure during an individual's pregnancy; some exposure misclassification seems likely. A number of different exposure-estimation techniques have been designed and implemented to address this challenge (18). This heterogeneity of exposure-assessment techniques that exists in the current literature makes it difficult to synthesize results. Different exposure estimation techniques may lead to different effect sizes. Few studies implemented more than one technique in unison on the same population, which would allow a comparison of the different estimates provided and the effect on risk estimates (14, 19).

The objective of this study was primarily to use a novel air pollution estimation technique with strong spatial and temporal resolution to estimate the effects from pollutants known to cause adverse health effects on pregnancy outcomes in a large Northwest (NW) England cohort from 2004-2008. In addition, a more traditional exposure assessment method of using nearest stationary air pollution monitors was implemented as a comparison technique.

Methods

Study design and cohort

A retrospective cohort study was conducted in NW England on births that occurred between 1 January 2004 and 31 December 2008. NW England has a total area of 5469 sq miles and a (2011) population of 7 052 000 (20). Some of the major cities within the region record some of the highest air pollution levels outside of London in the UK (21).

Maternal and perinatal data between 2004-2008 were obtained from the NW Perinatal Survey Unit (NWPSU). The NWPSU is based in Manchester and, during this time period, collected maternal and perinatal data at the time of delivery from 21 of the 29 maternity units in NW England. The eight units that were not included were generally small, and there was no difference between the index of multiple deprivation (IMD) score (based on hospital postcode) between the included and excluded maternity units. Data included: hospital site, ethnicity, postcode, region, mothers' date of birth, body mass index (BMI) at booking, parity, date of delivery, gestational age calculated from last menstrual period (LMP) and scan measurements, birth weight, multiple birth, live birth/stillbirth, type of delivery, and smoking. …

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