Effects of maternal exposure to particulate matter on birth weight by Parental Educational Attainment in Hong Kong

Abstract

Background: Associations between maternal exposure to air pollution and birth weight (BW) are inconsistent. Objectives: We assessed the associations between maternal exposure to fine particulate matter (PM2.5) and BW in different gestational windows. Methods: Spatio-temporal monthly PM2.5 concentrations in Tertiary Planning Units (TPU) were estimated by generalized additive models for years 2000-2011. Individual BW data 2001-2011 were obtained and the residential addresses of mothers were geocoded at TPU level. We assessed effects of PM2.5 on BW of all singleton births after adjusting for gender, numbers of children ever born alive, parental age and educational attainment by multiple linear regressions. Results: Monthly estimated PM2.5 concentrations ranged from 16.8 to 63.8 μg/m3. Of 356,810 singleton live births, 52% were male. The mean BW was 3159g. BW was not significantly related to maternal exposure to PM2.5 one month before delivery and in the third semester, but was significant for the entire pregnancy period (9 months), with a reduction of 9g (95% CI: 7g to 12g) for a 10 μg/m3 increase in PM2.5. In stratified analyses by educational attainment, association between PM2.5 and BW was not found in father’s or mother’s primary education attainment or below. However, the BW reduced to about 18g (95% CI: 13g, 23g) in the tertiary educational attainment or above. Conclusions: PM2.5 concentrations had an adverse effect on BW, in particular in parents with higher educational attainment. Further research on how the parental educational attainment affect the associations between PM2.5 and BW is needed.