Are cotinine assays of value in predicting adverse pregnancy outcome?

We investigated the utility of maternal cotinine concentration as a predictor of preterm and small-for-gestational-age (SGA) deliveries. Subjects were randomly selected from antenatal clinics, and their serum cotinine concentrations at approximately 16 weeks' gestation were compared with self-reports of smoking. The value of these measures in predicting preterm and SGA deliveries was examined, using likelihood ratios and logistic regression, for 845 women with singleton, live births. Smoking status alone (defined by self-report or cotinine) only weakly predicted preterm or SGA delivery. Self-reported moderate/high smoking (top 15% of smokers) had a likelihood ratio (LR) of 2 and a positive predictive value (PPV) of 17%. In contrast, moderate/high cotinine concentration (top 15% of smokers) had an LR of 5 and a PPV of 33%. The predictive value of cotinine was independent of associated maternal characteristics. Cotinine concentration may therefore be a useful predictor of poor pregnancy outcome, and should be considered as a screening tool.