title: Evaluation of the accuracy of self-reported smoking in pregnancy when the biomarker level in an active smoker is uncertain.
abstract: BACKGROUND
  Our main objective was to estimate smoking prevalence as well as sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of self-reported smoking among pregnant women in Edmonton, Canada, at 15-16 weeks of gestation.
  
  
  METHODS
  We used serum samples to assemble a cohort of pregnant women who underwent an optional second-trimester screening for chromosomal and developmental anomalies. We determined cotinine concentrations for 92 self-reported smokers (11% of the cohort) and for 285 self-reported nonsmoking mothers, using adapted urinary cotinine assay. Self-reports were collected at the time of delivery. In a validation study, serum cotinine was determined for known smokers and nonsmokers and used, within a Bayesian statistical framework, to define the distribution of cutoffs that differentiate true smokers from nonsmokers. This distribution of cutoffs was used to construct multiple two-by-two tables to obtain the distribution of sensitivity, specificity, PPV, NPV, and prevalence.
  
  
  RESULTS
  Sensitivity was poor (M = 47.4%, SD = 17.3%), but specificity was nearly perfect (M = 94.9%, SD = 1.1%). PPV (M = 66.6%, SD = 11.7%) was smaller than NPV (M = 84.7%, SD = 14.3%). In our sample, the prevalence of true smoking at 15-16 weeks of gestation was described by a skewed distribution with a mean of 21.6% (SD = 13.8%) and a median of 16.6%.
  
  
  CONCLUSIONS
  The strength of the present study includes blinding of subjects to the intention to test their sera for a biomarker of smoking. A limitation was the use of a nonrandom sample restricted to pregnancies that resulted in live births. We discuss data collection methods that would elicit more accurate smoking histories from pregnant women.
authors.affiliation: Community and Occupational Medicine Program, Department of Medicine, University of Alberta, 13-103E Clinical Sciences Building, Edmonton, Alberta T6G 2G3, Canada. iburstyn@ualberta.ca
authors.forename: Igor
authors.initials: I
authors.lastname: Burstyn
authors.forename: Nitin
authors.initials: N
authors.lastname: Kapur
authors.forename: Carol
authors.initials: C
authors.lastname: Shalapay
authors.forename: Fiona
authors.initials: F
authors.lastname: Bamforth
authors.forename: T Cameron
authors.initials: TC
authors.lastname: Wild
authors.forename: Juxin
authors.initials: J
authors.lastname: Liu
authors.forename: Don
authors.initials: D
authors.lastname: LeGatt
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D002170:Canada / Q000453:epidemiology; D015331:Cohort Studies; D003367:Cotinine / Q000097:blood*; D005260:Female; D006801:Humans; D008425:Maternal Behavior; D018811:Maternal Exposure / Q000706:statistics & numerical data*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000097:blood / Q000453:epidemiology*; D011295:Prenatal Care / Q000379:methods; D012016:Reference Values; D015203:Reproducibility of Results; D012650:Self Disclosure; D012680:Sensitivity and Specificity; D012907:Smoking / Q000097:blood / Q000453:epidemiology* / Q000523:psychology; D011795:Surveys and Questionnaires
chemical_list: D015415:Biomarkers; D003367:Cotinine