title: Hair biomarkers as measures of maternal tobacco smoke exposure and predictors of fetal growth.
abstract: BACKGROUND
  Most biomarker studies of the effects of maternal smoking on fetal growth have been based on a single blood or urinary cotinine value, which is inadequate in capturing maternal tobacco exposure over the entire pregnancy. We used hair biomarkers to compare the associations of maternal self-reported smoking, hair nicotine, and hair cotinine with birth weight for gestational age (BW for GA) among active and passive smokers during pregnancy.
  
  
  METHODS
  We collected maternal hair in the immediate postpartum period and measured nicotine and cotinine concentrations averaged over the pregnancy in 444 term controls drawn from 5,337 participants in a multicenter nested case-control study of preterm birth. BW for GA Z-score and small for gestational age (SGA) were based on Canadian population-based standards.
  
  
  RESULTS
  The addition of hair nicotine to multiple linear regression models containing self-reported active smoking, hair cotinine, or both explained significantly more variance in the BW for GA Z-score (p = .01, .03 and .04, respectively). Similarly, women with hair nicotine, but not cotinine, at or above the median value had a significant increase in the risk of SGA birth (odds ratio: 3.07, 95% CI: 1.25-7.52). No significant association was observed between maternal passive smoking and BW for GA based on hair biomarkers.
  
  
  CONCLUSIONS
  Hair nicotine is a better predictor of reductions in BW for GA than either hair cotinine or self-report. Our negative results for passive smoking suggest that previously reported small but significant effects may be explained by misclassification of active smokers as passive smokers based on self-report.
authors.affiliation: Department of Epidemiology, Biostatistics and Occupational Health, McGill University, 1140 Pine Avenue West, Montreal, Quebec H3A 1A3, Canada. nisha.almeida@mail.mcgill.ca
authors.forename: Nisha D
authors.initials: ND
authors.lastname: Almeida
authors.forename: Gideon
authors.initials: G
authors.lastname: Koren
authors.forename: Robert W
authors.initials: RW
authors.lastname: Platt
authors.forename: Michael S
authors.initials: MS
authors.lastname: Kramer
mesh_terms: D015415:Biomarkers / Q000032:analysis; D001724:Birth Weight; D002170:Canada; D016022:Case-Control Studies; D015331:Cohort Studies; D003367:Cotinine / Q000032:analysis / Q000493:pharmacokinetics*; D005260:Female; D047109:Fetal Development / Q000187:drug effects; D006197:Hair / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D018811:Maternal Exposure; D008431:Maternal-Fetal Exchange; D009538:Nicotine / Q000032:analysis / Q000493:pharmacokinetics*; D011247:Pregnancy / Q000378:metabolism*; D057566:Self Report; D012907:Smoking / Q000009:adverse effects / Q000378:metabolism*; D014028:Tobacco Smoke Pollution / Q000009:adverse effects
chemical_list: D015415:Biomarkers; D014028:Tobacco Smoke Pollution; D009538:Nicotine; D003367:Cotinine