Fetal exposure to tobacco smoke products: A comparison between self-reported maternal smoking and concentrations of cotinine and thiocyanate in cord serum

Background: The objective of the study was to assess the relationship between maternal smoking habits and biomarkers of tobacco smoke measured in cord serum. Methods: The study population comprised 102 mothers. 32 daily smokers, 24 occasional smokers and 136 nonsmokers. Information on maternal smoking habits was collected in a self-administered questionnaire at birth and compared with cotinine and thiocyanate concentrations in cord serum. Results: In linear regression analysis, a unit increase in daily cigarette smoking corresponded to a 4.4 ng/ml (95% CI: 1.1-7.6) increase in cotinine concentration and 2.3 mu mol/l(0.8-3.8) in thiocyanate. A cut-off point of 14 ng/ml cotinine separated well between daily smokers (88% above) and nonsmokers (96% below), but revealed a classification problem in occasional smokers (46% above). Conclusion: Cord serum cotinine and thiocyanate concentrations are related to daily smoking rate during pregnancy, but these concentrations vary considerably among occasional smokers. Detailed information on smoking habits is the key issue in understanding the adverse fetal effects of occasional smoking during pregnancy.