title: Smoke exposure, wheezing, and asthma development: a systematic review and meta-analysis in unselected birth cohorts.
abstract: BACKGROUND
  The understanding of the role of smoking exposure in the induction of wheezing and asthma in children is important for prevention.
  
  
  METHODS
  A systematic review of literature and a meta-analysis were conducted to identify studies on unselected prospective birth cohorts. The effect of exposure to maternal/parental smoking on the induction of current wheezing or asthma was evaluated in children aged 6 months, <6 years, and ≥6 years. Pooled odds ratios (OR) with 95% confidence intervals (CI) were estimated.
  
  
  RESULTS
  We identified 43 papers. Exposure to maternal prenatal smoking was associated with an increased risk of wheezing in <6-year-olds (OR 1.36; 95% CI: 1.19-1.55) and of wheezing or asthma in ≥6-year-olds (OR: 1.22, 95% CI: 1.03-1.44). A positive association (OR: 1.24, 95% CI: 1.11-1.38) was also found in the only three studies that evaluated exposure to maternal prenatal smoking alone. Postnatal exposures to maternal/parental smoking were associated with wheezing in <6-year-olds (OR: 1.21; 95% CI: 1.13-1.31 and OR: 1.30; 95% CI: 1.13-1.51), although it was often impossible to separate the role of postnatal from that of prenatal exposure; data in schoolchildren are limited and this precluded a meta-analysis. No clear association was found between exclusive postnatal exposure and wheezing or asthma.
  
  
  CONCLUSIONS
  We confirmed an important role of prenatal exposure to maternal smoking on the induction of wheezing and asthma in offspring, particularly in the first years of life. More studies with a consistent number of subjects only exposed to smoke postnatally are needed to better investigate the harmful effects on the induction of wheezing or asthma, particularly in schoolchildren.
authors.affiliation: Pediatric Pulmonology and Allergy Unit, Istituto Giannina Gaslini, Genoa, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Silvestri
authors.forename: Sara
authors.initials: S
authors.lastname: Franchi
authors.forename: Angela
authors.initials: A
authors.lastname: Pistorio
authors.forename: Loredana
authors.initials: L
authors.lastname: Petecchia
authors.forename: Franca
authors.initials: F
authors.lastname: Rusconi
mesh_terms: D001249:Asthma / Q000209:etiology*; D005260:Female; D006801:Humans; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D012135:Respiratory Sounds / Q000209:etiology*; D012907:Smoking / Q000009:adverse effects*; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*
chemical_list: D014028:Tobacco Smoke Pollution
keywords: adolescent; child; respiratory tract diseases; tobacco smoke pollution