title: The reduction of birth weight by fine particulate matter and its modification by maternal and neighbourhood-level factors: a multilevel analysis in British Columbia, Canada.
abstract: BACKGROUND
  The purpose of this research was to determine the relationship between modeled particulate matter (PM2.5) exposure and birth weight, including the potential modification by maternal risk factors and indicators of socioeconomic status (SES).
  
  
  METHODS
  Birth records from 2001 to 2006 (N = 231,929) were linked to modeled PM2.5 data from a national land-use regression model along with neighbourhood-level SES and socio-demographic data using 6-digit residential postal codes. Multilevel random coefficient models were used to estimate the effects of PM2.5, SES and other individual and neighbourhood-level covariates on continuous birth weight and test interactions. Gestational age was modeled with a random slope to assess potential neighbourhood-level differences of its effect on birth weight and whether any between-neighbourhood variability can be explained by cross-level interactions.
  
  
  RESULTS
  Models adjusted for individual and neighbourhood-level covariates showed a significant non-linear negative association between PM2.5 and birth weight explaining 8.5 % of the between-neighbourhood differences in mean birth weight. A significant interaction between SES and PM2.5 was observed, revealing a more pronounced negative effect of PM2.5 on birth weight in lower SES neighbourhoods. Further positive and negative modification of the PM2.5 effect was observed with maternal smoking, maternal age, gestational diabetes, and suspected maternal drug or alcohol use. The random intercept variance indicating between-neighbourhood birth weight differences was reduced by 75 % in the final model, while the random slope variance for between-neighbourhood gestational age effects remained virtually unchanged.
  
  
  CONCLUSIONS
  We provide evidence that neighbourhood-level SES variables and PM2.5 have both independent and interacting associations with birth weight, and together account for 49 % of the between-neighbourhood differences in birth weight. Evidence of effect modification of PM2.5 on birth weight across various maternal and neighbourhood-level factors suggests that certain sub-populations may be more or less vulnerable to relatively low doses PM2.5 exposure.
authors.affiliation: Division of Medical Sciences, University of Victoria, Medical Science Bld. Rm-104, PO Box 1700 STN CSC, Victoria, V8W 2Y2, BC, Canada.
authors.forename: Anders C
authors.initials: AC
authors.lastname: Erickson
authors.affiliation: Department of Geography, University of Victoria, David Turpin Bldg. Rm-B203, PO Box 1700 STN CSC, Victoria, V8W 2Y2, BC, Canada.
authors.forename: Aleck
authors.initials: A
authors.lastname: Ostry
authors.affiliation: Center for Advanced Research in Environmental Genomics, University of Ottawa, 20 Marie-Curie, Ottawa, K1N 6N5, ON, Canada.
authors.forename: Laurie H M
authors.initials: LH
authors.lastname: Chan
authors.affiliation: Division of Medical Sciences, University of Victoria, Medical Science Bld. Rm-104, PO Box 1700 STN CSC, Victoria, V8W 2Y2, BC, Canada. larbour@uvic.ca.|Department of Medical Genetics, University of British Columbia, C201 - 4500 Oak Street, Vancouver, V6H 3N1, BC, Canada. larbour@uvic.ca.
authors.forename: Laura
authors.initials: L
authors.lastname: Arbour
mesh_terms: D000293:Adolescent; D000328:Adult; D000393:Air Pollutants / Q000032:analysis*; D001724:Birth Weight; D001955:British Columbia; D002648:Child; D005260:Female; D006801:Humans; D018811:Maternal Exposure; D008875:Middle Aged; D008962:Models, Theoretical; D055361:Multilevel Analysis; D052638:Particulate Matter / Q000032:analysis*; D011247:Pregnancy; D012111:Residence Characteristics; D012959:Socioeconomic Factors; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter
keywords: Air pollution; Birth weight; Effect modification; Multilevel model; Neighbourhood effects; Particulate matter; Socioeconomic status