Smoking during pregnancy is associated with numerous adverse outcomes, including spontaneous abortion, preterm birth, low birth weight, fetal growth restriction, placental abruption, perinatal mortality and neurocognitive disorders.1,–,3 A large retrospective Australian cohort study suggests that women who quit smoking by 15 weeks of gestation have similar perinatal outcomes to women who have never smoked.4 This is in contrast to women who quit later in gestation, who have outcomes similar to those among continued smokers. Medical and societal pressures may make women who smoke during pregnancy reluctant to disclose their smoking behaviour. Accurate identification of pregnant smokers is imperative to offer effective smoking cessation programmes early enough to affect pregnancy outcomes.5

Several studies have compared self-reported smoking during pregnancy with …