title: Self-reported smoking status and plasma cotinine concentrations among pregnant women in the Norwegian Mother and Child Cohort Study.
abstract: BACKGROUND
  Underreporting of smoking in epidemiologic studies is common and may constitute a validity problem, leading to biased association measures. In this prospective study, we validated self-reported tobacco use against nicotine exposure assessed by plasma cotinine in the Norwegian Mother and Child Cohort Study (MoBa).
  
  
  METHODS
  The study was based on a subsample of 2,997 women in the MoBa study who delivered infants during the period 2002-2003. Self-reported tobacco use (test variable) and plasma cotinine concentrations (gold standard) were assessed at approximately gestational week 18.
  
  
  RESULTS
  Daily smoking was reported by 9% of the women, occasional smoking by 4%, and nonsmoking by 86% of the women. Sensitivity and specificity for self-reported smoking status were calculated using a cotinine cut-off estimated from the study population (30 nmol/l). Plasma cotinine concentrations ≥30 nmol/l were found in 94% of self-reported daily smokers, 66% of occasional smokers, and 2% of nonsmokers. After the numbers of self-reported nonsmokers with cotinine concentrations above the cut-off limit were added, the daily smoking prevalence increased from 9 to 11%. The sensitivity and specificity for self-reported daily smoking, using 30 nmol/l as the cut-off concentration, were 82 and 99%, respectively.
  
  
  CONCLUSIONS
  These findings suggest that self-reported tobacco use is a valid marker for tobacco exposure in the MoBa cohort.
authors.affiliation: Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway. Liv.Kvalvik@isf.uib.no
authors.forename: Liv G
authors.initials: LG
authors.lastname: Kvalvik
authors.forename: Roy M
authors.initials: RM
authors.lastname: Nilsen
authors.forename: Rolv
authors.initials: R
authors.lastname: Skjærven
authors.forename: Stein Emil
authors.initials: SE
authors.lastname: Vollset
authors.forename: Oivind
authors.initials: O
authors.lastname: Midttun
authors.forename: Per Magne
authors.initials: PM
authors.lastname: Ueland
authors.forename: Kjell
authors.initials: K
authors.lastname: Haug
mesh_terms: D000328:Adult; D015331:Cohort Studies; D003367:Cotinine / Q000097:blood*; D005260:Female; D006801:Humans; D009664:Norway / Q000453:epidemiology; D011247:Pregnancy; D011446:Prospective Studies; D057566:Self Report; D012680:Sensitivity and Specificity; D012907:Smoking / Q000097:blood* / Q000453:epidemiology*
chemical_list: D003367:Cotinine