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

## TL;DR

Maternal nicotine exposure during pregnancy, measured through urine cotinine, is linked to lower infant birth weight, with more cases than self-reported smoking.

## Contribution

This study demonstrates that urine cotinine measurements reveal higher nicotine exposure than self-reported data, impacting birth outcomes.

## Key findings

- Urine cotinine was detected in 50.4% of mothers, far exceeding the 16% who self-reported as smokers.
- Infants of mothers with nicotine in urine had significantly lower birth weights, especially females.

## Abstract

Objective: 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. Methods: We analysed data from 238 mother–neonate dyads. Smoking habits were recorded during routine prenatal check-ups and urine samples were collected to measure cotinine and creatinine levels. Results: Urine cotinine was detected in 50.4% (120/238) of women from the whole cohort, but only 16% (38/238) self-reported as smokers (chi-square 39.7, p < 0.0001), and these women had significantly smaller babies (p = 0.010). There was a significant negative correlation between maternal urine cotinine and birth weight (Spearman’s coefficient = −0.0226, p = 0.013). Female babies born to women with nicotine in their urine were significantly smaller (p = 0.001). Conclusions: Infant birth weight significantly reduced in mothers with exposure to nicotine during pregnancy. The number of women exposed to nicotine during late pregnancy (measured in urine) was markedly higher than self-reported and national smoking percentages, suggesting an urgent need for an improvement in medical record reporting on smoking habits to better assess neonatal outcomes.