title: Passive smoking in the etiology of non-syndromic orofacial clefts: a systematic review and meta-analysis.
abstract: BACKGROUND
  Studies have found a consistent positive association between maternal smoking and non-syndromic orofacial clefts (NSOFC). However, no comprehensive assessment of the association between NSOFC and passive smoking has been undertaken. This systematic review and meta-analysis explores the relationship between maternal passive smoking and NSOFC, and compares the associations between passive and active smoking.
  
  
  RESULTS
  Search strategy, inclusion / exclusion criteria, and data extraction from studies reporting maternal passive smoking and NSOFC was implemented without language restrictions. Risks of bias in the identified studies were assessed and this information was used in sensitivity analyses to explain heterogeneity. Meta-analysis and meta-regression of the extracted data were performed. Egger's test was used to test for small study effects. Fourteen eligible articles were identified. Maternal passive smoking exposure was associated with a twofold increase in risk of NSOFC (odds ratio: 2.11, 95% confidence interval: 1.54-2.89); this was apparent for both cleft lip with and without palate (OR: 2.05, 95% CI: 1.27-3.3) and cleft palate (OR: 2.11, 95% CI: 1.23-3.62). There was substantial heterogeneity between studies. In the studies that provided data enabling crude and adjusted odd ratios to be compared, adjustment for potential confounders attenuated the magnitude of association to about a 1.5-fold increase in risk.
  
  
  CONCLUSIONS
  Overall, maternal passive smoking exposure results in a 1.5 fold increase in risk of NSOFC, similar to the magnitude of risk reported for active smoking, but there is marked heterogeneity between studies. This heterogeneity is not explained by differences in the distribution of cleft types, adjustment for covariates, broad geographic region, or study bias/quality. This thorough meta-analysis provides further evidence to minimize exposure to environmental tobacco smoke in policy making fora and in health promotion initiatives.
authors.affiliation: Pediatric Dentistry Department, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia; Department of Oral Health Sciences, University of Dundee, Dundee, Scotland, United Kingdom.
authors.forename: Heba J
authors.initials: HJ
authors.lastname: Sabbagh
authors.affiliation: Department of Dental Public Health, Faculty of Dentistry Kind Abdulaziz University, Jeddah, Saudi Arabia; Department of Biostatistics, High Institute of Public Health, Alexandria University. Alexandria, Egypt.
authors.forename: Mona Hassan Ahmed
authors.initials: MH
authors.lastname: Hassan
authors.affiliation: Paediatric Dentistry, Department of Oral Health Sciences, University of Dundee, Dundee, Scotland, United Kingdom.
authors.forename: Nicola P T
authors.initials: NP
authors.lastname: Innes
authors.affiliation: Pediatric Dentistry Department, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia; Faculty of Dental Medicine (Girls' Branch), Al Azhar University, Cairo, Egypt.
authors.forename: Heba M
authors.initials: HM
authors.lastname: Elkodary
authors.affiliation: Human Genome Epidemiology, School of Epidemiology, Public Health and Preventive Medicine, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Julian
authors.initials: J
authors.lastname: Little
authors.affiliation: Division of Oral Health Sciences and WHO Collaborating Centre for Oral Health & Craniofacial Anomalies, University of Dundee, Dundee, Scotland, United Kingdom.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Mossey
mesh_terms: D001921:Brain / Q000002:abnormalities*; D002971:Cleft Lip / Q000209:etiology*; D002972:Cleft Palate / Q000209:etiology*; D005260:Female; D006801:Humans; D018811:Maternal Exposure / Q000009:adverse effects*; D008431:Maternal-Fetal Exchange; D016017:Odds Ratio; D011247:Pregnancy; D012044:Regression Analysis; D012307:Risk Factors; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*
chemical_list: D014028:Tobacco Smoke Pollution