Evaluation of the accuracy of self-reported smoking in pregnancy when the biomarker level in an active smoker is uncertain.
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.
Burstyn
Igor
I
Community and Occupational Medicine Program, Department of Medicine, University of Alberta, 13-103E Clinical Sciences Building, Edmonton, Alberta T6G 2G3, Canada. iburstyn@ualberta.ca
Kapur
Nitin
N
Shalapay
Carol
C
Bamforth
Fiona
F
Wild
T Cameron
TC
Liu
Juxin
J
LeGatt
Don
D
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
D015415:Biomarkers; D003367:Cotinine