Cigarette consumption and biomarkers of nicotine exposure during pregnancy and postpartum.

BACKGROUND AND AIMS: Smokers can regulate their nicotine intake by altering the number of cigarettes smoked per day (CPD) and their smoking intensity. The current study aimed to compare the utility of self-reported CPD, total nicotine equivalents (TNE) and urinary cotinine to estimate nicotine intake during pregnancy. DESIGN: Longitudinal smoking behavior and biomarker data were collected at early pregnancy, late pregnancy and at postpartum as part of a smoking cessation trial to examine voucher-based incentives for decreasing smoking. SETTING: Obstetric practices in Burlington, Vermont, United States. PARTICIPANTS: A subset of participants (n = 47) from the parent trial, recruited between December 2006 and June 2012, who provided a urine sample at each assessment during early pregnancy, late pregnancy and postpartum. MEASUREMENTS: Smoking was assessed using self-reported CPD, TNE, TNE/CPD and urinary cotinine. FINDINGS: Pregnant smokers reported smoking 10.4 CPD at early pregnancy, 7.2 CPD at late pregnancy (a 31% reduction at late pregnancy, P = 0.001) and 8.6 CPD at postpartum (a 19% increase from late pregnancy, P = 0.08). TNE exposure was 41% (P = 0.07) and 48% (P = 0.03) lower at early and late pregnancy, respectively, compared to postpartum. TNE/CPD was on average 167% higher at late pregnancy compared to early pregnancy (P = 0.01) and remained high at postpartum, where it was 111% higher compared to early pregnancy (P = 0.007). Uriniary cotinine underestimated nicotine intake by 55% during early pregnancy and by 65% during late pregnancy compared to postpartum (P(interaction)  < 0.001); the underestimation was greater in slower (P(interaction)  < 0.001) versus faster (P(interaction)  = 0.04) nicotine metabolizers. CONCLUSIONS: Neither cigarettes smoked per day (CPD) nor cotinine provides an accurate estimate of nicotine exposure during pregnancy. CPD underestimates nicotine intake substantially due to under-reporting and/or higher intensity of smoking, while cotinine underestimates nicotine intake markedly due to accelerated nicotine (and cotinine) metabolism during pregnancy.