Smoking during pregnancy is the single most preventable cause of illness and death among mothers and infants. Because of the stigma associated with tobacco use during pregnancy, pregnant women are less likely to disclose their smoking status to doctors or study researchers. This study will evaluate the use of a new biomarker of nicotine metabolism to estimate tobacco use in a group of pregnant women who participated in the New England Smoking Cessation and Reduction in Pregnancy Trial (SCRIPT).