Correlation between self-reported smoking status and serum cotinine during pregnancy.

Maternal smoking is associated with adverse perinatal outcomes. Because of concerns of underreporting, investigators routinely perform biochemical testing to confirm smoking status, such as serum cotinine, a major metabolite of nicotine, adding an increased cost to examine compliance. The objectives of this study were to determine the sensitivity and specificity of self-reported smoking with serum cotinine as the gold standard and to determine the correlation between self-reported smoking in cigarettes per day and serum cotinine levels. In this cross-sectional study, we surveyed women during the first trimester of pregnancy on their tobacco exposure. A total of 40 women reported that they were smokers, and 40 were nonsmokers, 1 of whom had quit 5 days prior. The mean (+/-S.D.) serum cotinine value among smokers was 155 (+/-122) ng/l, vs. 1 (+/-6) ng/l in nonsmokers, p<0.001. The sensitivity of self-reported smoking status was 97.6%, and the specificity was 100%. Comparing the reported number of cigarettes smoked and the serum cotinine level, the Spearman correlation coefficient was 0.92 (p=0.015) overall and 0.67 (p=0.088) for the subgroup of smokers. This study demonstrates that self-reported smoking exposure during pregnancy is highly accurate. The high correlation coefficient suggests that this is a robust surrogate for cotinine levels.