title: In utero exposure to maternal smoking and women's risk of fetal loss in the Norwegian Mother and Child Cohort (MoBa).
abstract: BACKGROUND
  Whether in utero exposure to tobacco smoke increases a woman's risk of fetal loss later in life is unknown, though data on childhood exposure suggest an association may exist. This study evaluated the association between in utero exposure to tobacco smoke and fetal loss in the Norwegian Mother and Child Cohort Study (MoBa), which enrolled ∼40% of the pregnant women in Norway from 1999 to 2008.
  
  
  METHODS
  Information on exposure to tobacco smoke in utero, the woman's own smoking behavior during pregnancy and other factors was obtained by a questionnaire completed at ∼17 weeks of gestation. Subsequent late miscarriage (fetal death <20 weeks) and stillbirth (fetal death ≥ 20 weeks) were ascertained from the Norwegian Medical Birth Registry. This analysis included 76 357 pregnancies (MoBa data set version 4.301) delivered by the end of 2008; 59 late miscarriages and 270 stillbirths occurred. Cox proportional hazards models were fit for each outcome and for all fetal deaths combined.
  
  
  RESULTS
  The adjusted hazard ratio (HR) of late miscarriage was 1.23 [95% confidence interval (CI), 0.72-2.12] in women with exposure to maternal tobacco smoke in utero when compared with non-exposed women. The corresponding adjusted HR for stillbirths was 1.11 (95% CI, 0.85-1.44) and for all fetal deaths combined, it was 1.12 (95% CI, 0.89-1.43).
  
  
  CONCLUSIONS
  The relatively wide CI around the HR for miscarriage reflected the limited power to detect an association, due to enrollment around 17 weeks of gestation. However, for in utero exposure to tobacco smoke and risk of stillbirth later in life, where the study power was adequate, our data provided little support for an association.
authors.affiliation: Epidemiology Branch, National Institute of Environmental Health Sciences NIH/DHHS/USA, MD A3-05, 111 TW Alexander Dr, Research Triangle Park, NC 27709, USA. cupuluicabl@niehs.nih.gov
authors.forename: L A
authors.initials: LA
authors.lastname: Cupul-Uicab
authors.forename: D D
authors.initials: DD
authors.lastname: Baird
authors.forename: R
authors.initials: R
authors.lastname: Skjaerven
authors.forename: P
authors.initials: P
authors.lastname: Saha-Chaudhuri
authors.forename: K
authors.initials: K
authors.lastname: Haug
authors.forename: M P
authors.initials: MP
authors.lastname: Longnecker
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology*; D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D005313:Fetal Death / Q000453:epidemiology*; D006801:Humans; D053208:Kaplan-Meier Estimate; D018811:Maternal Exposure / Q000706:statistics & numerical data; D009664:Norway / Q000453:epidemiology; D011247:Pregnancy; D012907:Smoking / Q000009:adverse effects*