Exposure to environmental tobacco smoke in pregnant women: The association between self-report and serum cotinine

The risk of delivering a low-birth-weight infant as the result of exposing a nonsmoking pregnant woman to environmental tobacco smoke (ETS) is not well defined. The method of ascertaining ETS exposure during pregnancy may explain the lack of consistent study findings. In a large sample of pregnant women, we compared distributions between two methods of ETS exposure: self-report and cotinine, a nicotine metabolite, from serum. At delivery, subjects were asked about duration and location of exposure to ETS during their second trimester. A single cotinine measurement was assayed from serum collected at 15-19 weeks gestation (limit of detection = 0.05 ng/mL). Self-reported (hours per day) ETS exposure was correlated (r = 0.38) with cotinine concentration. Regression analysis revealed that while self-reported ETS was significantly associated with (log) cotinine, it did not explain a large amount of total variation. While 72% of subjects reported no exposure to ETS, almost all had measurable levels of cotinine. Studies of pregnant women based upon an hours per day ETS question have likely misclassified a sizable portion of ETS-exposed women as "unexposed." Since there is recent evidence that low levels of ETS exposure result in unfavorable pregnancy outcomes, these studies have underestimated the effect of ETS. (C) 2002 Elsevier Science (USA).