title: Maternal smoking in pregnancy and asthma in preschool children: a pooled analysis of eight birth cohorts.
abstract: BACKGROUND
  Although epidemiological studies suggest that exposure to maternal smoking during fetal and early life increases the risk of childhood wheezing and asthma, previous studies were not able to differentiate the effects of prenatal from postnatal exposure.
  
  
  OBJECTIVE
  To assess the effect of exposure to maternal smoking only during pregnancy on wheeze and asthma among preschool-age children.
  
  
  METHODS
  A pooled analysis was performed based on individual participant data from eight European birth cohorts. Cohort-specific effects of maternal smoking during pregnancy, but not during the first year, on wheeze and asthma at 4 to 6 years of age were estimated using logistic regression and then combined using a random effects model. Adjustments were made for sex, parental education, parental asthma, birth weight, and siblings.
  
  
  RESULTS
  Among the 21,600 children included in the analysis, 735 children (3.4%) were exposed to maternal smoking exclusively during pregnancy but not in the first year after birth. In the pooled analysis, maternal smoking only during pregnancy was associated with wheeze and asthma at 4 to 6 years of age, with adjusted odds ratios of 1.39 (95% confidence interval, 1.08-1.77) and 1.65 (95% confidence interval, 1.18-2.31), respectively. The likelihood to develop wheeze and asthma increased statistically significantly in a linear dose-dependent manner in relation to maternal daily cigarette consumption during the first trimester of pregnancy.
  
  
  CONCLUSIONS
  Maternal smoking during pregnancy appears to increase the risk of wheeze and asthma among children who are not exposed to maternal smoking after birth.
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Box 210, SE-171 77 Stockholm, Sweden.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Neuman
authors.forename: Cynthia
authors.initials: C
authors.lastname: Hohmann
authors.forename: Nicola
authors.initials: N
authors.lastname: Orsini
authors.forename: Göran
authors.initials: G
authors.lastname: Pershagen
authors.forename: Esben
authors.initials: E
authors.lastname: Eller
authors.forename: Henrik Fomsgaard
authors.initials: HF
authors.lastname: Kjaer
authors.forename: Ulrike
authors.initials: U
authors.lastname: Gehring
authors.forename: Raquel
authors.initials: R
authors.lastname: Granell
authors.forename: John
authors.initials: J
authors.lastname: Henderson
authors.forename: Joachim
authors.initials: J
authors.lastname: Heinrich
authors.forename: Susanne
authors.initials: S
authors.lastname: Lau
authors.forename: Mark
authors.initials: M
authors.lastname: Nieuwenhuijsen
authors.forename: Jordi
authors.initials: J
authors.lastname: Sunyer
authors.forename: Christina
authors.initials: C
authors.lastname: Tischer
authors.forename: Maties
authors.initials: M
authors.lastname: Torrent
authors.forename: Ulrich
authors.initials: U
authors.lastname: Wahn
authors.forename: Alet H
authors.initials: AH
authors.lastname: Wijga
authors.forename: Magnus
authors.initials: M
authors.lastname: Wickman
authors.forename: Thomas
authors.initials: T
authors.lastname: Keil
authors.forename: Anna
authors.initials: A
authors.lastname: Bergström
mesh_terms: D001249:Asthma / Q000209:etiology*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007223:Infant; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D012135:Respiratory Sounds / Q000209:etiology; D012907:Smoking / Q000009:adverse effects*