Beschreibung:
<jats:title>Abstract</jats:title><jats:p><jats:italic>Background</jats:italic>. Objective validation of smoking status is necessary. Earlier studies have used saliva cotinine concentrations between 14.2 and 30 ng/ml as cut‐off values to distinguish pregnant smokers from non‐smokers. However, these cut‐offs derive from studies including men and non‐pregnant women. This constitutes a problem, as recent studies have reported an accelerated metabolism in pregnant smokers. The aim of this study was to determine the optimum cut‐off cotinine level distinguishing pregnant smokers from pregnant non‐smokers. <jats:italic>Methods</jats:italic>. An observational study of 620 pregnant women, 359 self‐reported smokers and 261 self‐reported non‐smokers, with complete data on smoking status and saliva cotinine. The study was conducted at a large university hospital in Copenhagen, Denmark. Saliva was sampled at the first antenatal visit to the midwife and analyzed for cotinine level by gas chromatography. Participants completed a questionnaire immediately after the first visit. <jats:italic>Results</jats:italic>. A saliva cotinine cut‐off level of 13 ng/ml, corresponding to a sensitivity of 0.99 and specificity 0.98, was found to be the optimum cut‐off value separating pregnant smokers from non‐smokers. The sum of the sensitivity and specificity was at its maximum, 1.981. A 95% bootstrap confidence interval for the optimum cut‐off was (8–14 ng/ml). <jats:italic>Conclusion</jats:italic>. From the present data we recommend that in future studies on smoking cessation and pregnancy a cut‐off level of 13 ng/ml should be applied to distinguish between pregnant smokers and non‐smokers.</jats:p>