Figure 1.

Categorization of the study population into four tobacco exposure groups, depicting the correlation between plasma cotinine concentrations and self-reported tobacco exposure. The grouping was primarily based on plasma cotinine concentrations (Groups 1 and 2 had cotinine levels below the limit of detection (LOD) of 0.17 ng/ml, Group 3: 0.17-13.99 ng/ml, Group 4: >14 ng/ml). Those with cotinine below the LOD were further divided into two groups based on self-reported history: Group 1 comprised those who had never smoked and had not been exposed to environmental tobacco smoke (ETS) [None], and Group 2 comprised those who were self-reported active smokers at 26-28 weeks’ gestation [smoker], those who had smoked regularly during the one year prior to conception [periconception smoker], and those who were exposed to ETS at home or at work. Self-reported history in Groups 3 and 4 are indicated here, although it was not used as criteria for categorization. The number of subjects in each subgroup within each category is shown in the accompanying table.