title: Changes in the rate of nicotine metabolism across pregnancy: a longitudinal study.
abstract: OBJECTIVE
  Increased nicotine metabolism during pregnancy could explain why nicotine replacement therapy (NRT) appears to be less effective on smoking cessation in pregnancy than in non-pregnant smokers, but little is known about nicotine metabolism across pregnancy. This study was conducted to determine when changes in nicotine metabolism occur during pregnancy and to describe the magnitude of these changes.
  
  
  METHODS
  Longitudinal cohort study of pregnant smokers' nicotine metabolite ratio (NMR).
  
  
  METHODS
  101 pregnant smokers recruited from hospital antenatal clinics in Nottingham, UK were asked to provide saliva samples at 8-14 weeks (n = 98), 18-22 weeks (n = 65), 32-36 weeks gestation (n = 47), 4 weeks postpartum (n = 44) and 12 weeks postpartum (n = 47).
  
  
  METHODS
  Nicotine metabolite ratio (NMR) was measured using the ratio of cotinine to its primary metabolite trans-3'-hydroxycotinine. Multi-level modelling was used to detect any overall difference in NMR between time points. The 12 week postpartum NMR was compared with the NMRs collected antenatally and 4 weeks postpartum.
  
  
  RESULTS
  NMR changed over time (p = 0.0006). Compared with NMR at 12 weeks postpartum, NMR was significantly higher at 18-22 weeks (26% higher, 95% CI 12% to 38%) and 32-36 weeks (23% higher, 95% CI 9% to 35%). There was no significant difference between the 8-14 weeks gestation or 4 weeks postpartum NMR and 12 weeks postpartum.
  
  
  CONCLUSIONS
  Nicotine metabolism appears to be faster during pregnancy; this faster metabolism is apparent from 18 to 22 weeks of pregnancy and appears to fall by 4 weeks after childbirth.
authors.affiliation: UK Centre for Tobacco and Alcohol Studies and NIHR School for Primary Care Research, Division of Primary Care, University of Nottingham Medical School, Nottingham, UK.
authors.forename: Katharine
authors.initials: K
authors.lastname: Bowker
authors.affiliation: UK Centre for Tobacco and Alcohol Studies, Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK.
authors.forename: Sarah
authors.initials: S
authors.lastname: Lewis
authors.affiliation: UK Centre for Tobacco and Alcohol Studies and NIHR School for Primary Care Research, Division of Primary Care, University of Nottingham Medical School, Nottingham, UK.
authors.forename: Tim
authors.initials: T
authors.lastname: Coleman
authors.affiliation: UK Centre for Tobacco and Alcohol Studies and NIHR School for Primary Care Research, Division of Primary Care, University of Nottingham Medical School, Nottingham, UK.
authors.forename: Sue
authors.identifier: http://orcid.org/0000-0002-1994-6395
authors.initials: S
authors.lastname: Cooper
mesh_terms: D000328:Adult; D002853:Chromatography, Liquid; D003367:Cotinine / Q000031:analogs & derivatives / Q000378:metabolism; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D055361:Multilevel Analysis; D009538:Nicotine / Q000378:metabolism*; D049590:Postpartum Period / Q000378:metabolism*; D011247:Pregnancy / Q000378:metabolism*; D011261:Pregnancy Trimester, First / Q000378:metabolism; D011262:Pregnancy Trimester, Second / Q000378:metabolism; D011263:Pregnancy Trimester, Third / Q000378:metabolism; D012463:Saliva / Q000737:chemistry; D012907:Smoking / Q000378:metabolism*; D053719:Tandem Mass Spectrometry; D006113:United Kingdom; D055815:Young Adult
chemical_list: C001381:hydroxycotinine; D009538:Nicotine; D003367:Cotinine
keywords: Antenatal; metabolism; nicotine; postpartum; pregnancy; smoking