The Relationship between Maternal Smoking and Infant Birth Weight: Improving Accuracy through Urine Cotinine Analysis and Effective Medical Record Strategies

We conducted a study to determine if antenatally collected maternal urine cotinine (a me- 13 tabolite of nicotine) measurements can be used to assess the neonatal impact of nicotine exposure 14 during pregnancy. This was a prospective longitudinal cohort of mother-infant dyads. Only term 15 singleton pregnancies were included. The primary outcome measure was the correlation between 16 maternal urine cotinine and infant birth weight. We analysed data from 238 mother-neonates' dy- 17 ads. Urine cotinine was detected in 50.4 % (120/238) women from the whole cohort, but only 16% 18 (38/238) self-reported as smokers (chi-square 39.7, p<0.0001), and these women had significantly 19 smaller babies (p=0.010). There was a significant negative correlation between maternal urine co- 20 tinine and birth weight (Spearman's coefficient = -0.0226, p=0.013). Female babies born to women 21 with nicotine in the urine were significantly smaller (p= 0.001). The number of women exposed to 22 nicotine during late pregnancy (measured in urine) was markedly higher than self-reported and 23 National smoking percentages, suggesting an urgent need for improvement of medical record re- 24 porting on smoking habits to better assess neonatal outcomes.