Introduction: Pregnant women often underreport their smoking status and extent of secondhand smoke (SHS) exposure. Biomarker confirmation is the recommended method to assess smoking behaviors and SHS exposure in both mothers and infants. objectives: The primary aims are to (a) examine the relationship between smoking behaviors and SHS exposure in mother-baby couplets using maternal and infant hair nicotine and maternal urine cotinine analyses and (b) determine whether there is an association between maternal and infant hair nicotine samples obtained shortly after birth.A cross-sectional study with a multiethnic sample of 210 mother-baby couplets assessing SHS exposure. Results: The level of maternal hair nicotine (MHN) was significantly different among three groups: nonsmoking, nonsmoking/passive exposed, and smoking (p < .0001), with nonsmoking and nonexposed women having the lowest level. Urine cotinine was strongly associated with self-reported smoking status (ρ = .88; p < .0001). Maternal and infant hair nicotine were correlated, although MHN correlated more strongly with smoking status (r = .46, p < .0001) than infant hair nicotine (r = .39, p < .0001). Conclusion: MHN was a more precise biomarker of prenatal SHS exposure than infant hair nicotine; mothers' urine cotinine was strongly correlated with self-reported smoking status.
