Trimester effects of source-specific PM₁₀ on birth weight outcomes in the Avon Longitudinal Study of Parents and...

Evidence suggests that exposure to particulate matter with aerodynamic diameter less than 10 microm (PM₁₀) is associated with reduced birth weight, but information is limited on the sources of PM₁₀ and exposure misclassification from assigning exposures to place of residence at birth.

Trimester and source-specific PM₁₀ exposures (PM₁₀ from road source, local non-road source, and total source) in pregnancy were estimated using dispersion models and a full maternal residential history for 12,020 births from the Avon longitudinal study of parents and children (ALSPAC) cohort in 1990-1992 in the Bristol area. Information on birth outcomes were obtained from birth records. Maternal sociodemographic and lifestyle factors were obtained from questionnaires. We used linear regression models for continuous outcomes (birth weight, head circumference (HC), and birth length (BL) and logistic regression models for binary outcomes (preterm birth (PTB), term low birth weight (TLBW) and small for gestational age (SGA)). Sensitivity analysis was performed using multiple imputation for missing covariate data.

After adjustment, interquartile range increases in source specific PM₁₀ from traffic were associated with 17 to 18% increased odds of TLBW in all pregnancy periods. We also found odds of TLBW increased by 40% (OR: 1.40, 95%CI: 1.12, 1.75) and odds of SGA increased by 18% (OR: 1.18, 95%CI: 1.05, 1.32) per IQR (6.54 microg/m³) increase of total PM₁₀ exposure in the third trimester.

This study adds to evidence that maternal PM₁₀ exposures affect birth weight, with particular concern in relation to exposures to PM₁₀ from road transport sources; results for total PM₁₀ suggest greatest effect in the third trimester. Effect size estimates relate to exposures in the 1990s and are higher than those for recent studies - this may relate to reduced exposure misclassification through use of full residential history information, changes in air pollution toxicity over time and/or residual confounding.