Impact of London's road traffic air and noise pollution on birth weight: retrospective population based cohort study.

To investigate the relation between exposure to both air and noise pollution from road traffic and birth weight outcomes. Retrospective population based cohort study. Greater London and surrounding counties up to the M25 motorway (2317 km), UK, from 2006 to 2010. 540 365 singleton term live births. Term low birth weight (LBW), small for gestational age (SGA) at term, and term birth weight. Average air pollutant exposures across pregnancy were 41 μg/m nitrogen dioxide (NO), 73 μg/m nitrogen oxides (NO), 14 μg/m particulate matter with aerodynamic diameter <2.5 μm (PM), 23 μg/m particulate matter with aerodynamic diameter <10 μm (PM), and 32 μg/m ozone (O). Average daytime (L) and night-time (L) road traffic A-weighted noise levels were 58 dB and 53 dB respectively. Interquartile range increases in NO, NO, PM, PM, and source specific PM from traffic exhaust (PM) and traffic non-exhaust (brake or tyre wear and resuspension) (PM) were associated with 2% to 6% increased odds of term LBW, and 1% to 3% increased odds of term SGA. Air pollutant associations were robust to adjustment for road traffic noise. Trends of decreasing birth weight across increasing road traffic noise categories were observed, but were strongly attenuated when adjusted for primary traffic related air pollutants. Only PM and PM were consistently associated with increased risk of term LBW after adjustment for each of the other air pollutants. It was estimated that 3% of term LBW cases in London are directly attributable to residential exposure to PM>13.8 μg/mduring pregnancy. The findings suggest that air pollution from road traffic in London is adversely affecting fetal growth. The results suggest little evidence for an independent exposure-response effect of traffic related noise on birth weight outcomes.