Place of work and residential exposure to ambient air pollution and birth outcomes in Scotland, using geographically fine pollution climate mapping estimates

OBJECTIVES A relationship between ambient air pollution and adverse birth outcomes has been found in a large number of studies that have mainly used a nearest monitor methodology. Recent research has suggested that the effect size may have been underestimated in these studies. This paper examines associations between birth outcomes and ambient levels of residential and workplace sulphur dioxide, particulates and Nitrogen Dioxide estimated using an alternative method - pollution climate mapping. METHODS Risk of low birthweight and mean birthweight (for n=21,843 term births) and risk of preterm birth (for n=23,086 births) were modelled against small area annual mean ambient air pollution concentrations at work and residence location adjusting for potential confounding factors for singleton live births (1994-2008) across Scotland. RESULTS Odds ratios of low birthweight of 1.02 (95% CI, 1.01-1.03) and 1.07 (95% CI, 1.01-1.12) with concentration increases of 1 µg/m(3) for NO2 and PM10 respectively. Raised but insignificant risks of very preterm birth were found with PM10 (relative risk ratio=1.08; 95% CI, 1.00 to 1.17 per 1 µg/m(3)) and NO2 (relative risk ratio=1.01; 95% CI, 1.00 to 1.03 per 1 µg/m(3)). An inverse association between mean birthweight and mean annual NO2(-1.24 g; 95% CI, -2.02 to -0.46 per 1 µg/m(3)) and PM10 (-5.67 g; 95% CI, -9.47 to -1.87 per 1 µg/m(3)). SO2 showed no significant associations. CONCLUSIONS This study highlights the association between air pollution exposure and reduced newborn size at birth. Together with other recent work it also suggests that exposure estimation based on the nearest monitor method may have led to an under-estimation of the effect size of pollutants on birth outcomes.