Ambient Air Pollution and Newborn Size and Adiposity at Birth: Differences by Maternal Ethnicity (the Born in Bradford Study Cohort)

BACKGROUND: Exposure to ambient air pollution has been associated with reduced newborn's size, however the modifying effect of maternal ethnicity remains little explored among South Asians. OBJECTIVES: To investigate ethnic differences in the association between ambient air pollution and newborn's size. METHOD: Pregnant women were recruited between 2007 and 2010 for the Born in Bradford cohort study, in England. Exposures to particulate matter (<= 10 mu m, PM10, <= 2.5 mu m, PM2.5), PM2.5 absorbance and nitrogen oxides (NOx, NO2) were estimated using land-use regressions models. Effect modification by maternal ethnicity ("White British" or "Pakistani origin", self-reported) on the associations of air pollution and birth weight, head circumference, and triceps and subscapular skinfold thickness was evaluated using multivariate linear regression models. RESULTS: A 5-mu g/m(3) increase in mean third trimester PM2.5 was associated with significantly lower birth weight and smaller head circumference in children of White British mothers (-43g; 95% CI: -76, -10 and -0.28cm; 95% CI: -0.39, -0.17, respectively), but not in children of Pakistani origin (9g; 95% CI: -17, 35 and -0.08cm; 95% CI: -0.17, 0.01, respectively) (Pint= 0.03 and <0.001). In contrast, PM2.5 was associated with significantly larger triceps and subscapular skinfold thicknesses in children of Pakistani origin (0.17mm; 95% CI: 0.08, 0.25 and 0.21mm; 95% CI: 0.12, 0.29, respectively), but not in White British children (-0.02mm; 95% CI: -0.14, 0.01 and 0.06mm 95% CI: -0.06, 0.18, respectively) (P-int= 0.06 and 0.11). Patterns of associations for PM10 and PM2.5 absorbance according to ethnicity were similar to PM2.5, while associations of the outcomes with NO2 and NOx were mostly non-significant in both ethnic groups. CONCLUSIONS: Our results suggest that associations of ambient PM exposures with newborn size and adiposity differ between White British and Pakistani origin infants.