Accuracy of prenatal smoking data from Washington State birth certificates in a population-based sample with cotinine measurements

Purpose: To assess the accuracy of smoking data in contemporary U.S. birth certificates. Methods: We compared data on prenatal smoking as reported on Washington State birth certificates to cotinine measured in archived newborn screening dried blood spots for 200 infants born in 2007 (100 randomly selected from births to self-reported nonsmokers and 100 born to self-reported smokers). We estimated the sensitivity of the birth certificate data to identify prenatal smokers and the precision with which self-identified third trimester smokers report smoking levels. Results: Infants born to two (2%) mothers who reported they did not smoke during the pregnancy had whole blood cotinine concentrations consistent with active smoking by the mother (sensitivity 85%). Sensitivity of the birth certificate to identify reported smokers who continued to smoke throughout pregnancy was similar (89%). Among self-identified third trimester smokers whose infants' specimens were collected shortly after delivery, Spearman rho between infant cotinine and maternal-reported cigarettes/day in the third trimester was 0.54. Conclusions: Birth certificates may represent a viable option for assessing prenatal smoking status, and possibly smoking cessation and level among smokers, in epidemiologic studies sufficiently powered to overcome a moderate amount of exposure measurement error.