To confirm pregnancy status, quality screens checked for consistent self-reported gestational age, last menstrual period, estimated due date, and reports of real vs sham pregnancy symptoms. Quality screens for smoking status included knowing the number of cigarettes in a pack, experience of head rush when smoking (not typical for a regular smoker), and consistent reporting of smoking intensity. Additional quality screens included flagging when a respondent provided the same answers in a matrix of questions (ie, clicked answers in a straight vertical line down the page).