We conducted a study to determine if antenatally collected maternal urine cotinine (a metabolite of nicotine) measurements can be used to assess the neonatal impact of nicotine exposure during pregnancy. This was a prospective longitudinal cohort of mother-infant dyads. Only term singleton pregnancies were included. The primary outcome measure was the correlation between maternal urine cotinine and infant birth weight. We analysed data from 238 mother-neonates' dyads. Urine cotinine was detected in 50.4 % (120/238) women from the whole cohort, but only 16% (38/238) self-reported as smokers (chi-square 39.7, p