title: Associations between maternal periconceptional exposure to secondhand tobacco smoke and major birth defects.
abstract: BACKGROUND
  While associations between secondhand smoke and a few birth defects (namely, oral clefts and neural tube defects) have been noted in the scientific literature, to our knowledge, there is no single or comprehensive source of population-based information on its associations with a range of birth defects among nonsmoking mothers.
  
  
  OBJECTIVE
  We utilized data from the National Birth Defects Prevention Study, a large population-based multisite case-control study, to examine associations between maternal reports of periconceptional exposure to secondhand smoke in the household or workplace/school and major birth defects.
  
  
  METHODS
  The multisite National Birth Defects Prevention Study is the largest case-control study of birth defects to date in the United States. We selected cases from birth defect groups having >100 total cases, as well as all nonmalformed controls (10,200), from delivery years 1997 through 2009; 44 birth defects were examined. After excluding cases and controls from multiple births and whose mothers reported active smoking or pregestational diabetes, we analyzed data on periconceptional secondhand smoke exposure-encompassing the period 1 month prior to conception through the first trimester. For the birth defect craniosynostosis, we additionally examined the effect of exposure in the second and third trimesters as well due to the potential sensitivity to teratogens for this defect throughout pregnancy. Covariates included in all final models of birth defects with ≥5 exposed mothers were study site, previous live births, time between estimated date of delivery and interview date, maternal age at estimated date of delivery, race/ethnicity, education, body mass index, nativity, household income divided by number of people supported by this income, periconceptional alcohol consumption, and folic acid supplementation. For each birth defect examined, we used logistic regression analyses to estimate both crude and adjusted odds ratios and 95% confidence intervals for both isolated and total case groups for various sources of exposure (household only; workplace/school only; household and workplace/school; household or workplace/school).
  
  
  RESULTS
  The prevalence of secondhand smoke exposure only across all sources ranged from 12.9-27.8% for cases and 14.5-15.8% for controls. The adjusted odds ratios for any vs no secondhand smoke exposure in the household or workplace/school and isolated birth defects were significantly elevated for neural tube defects (anencephaly: adjusted odds ratio, 1.66; 95% confidence interval, 1.22-2.25; and spina bifida: adjusted odds ratio, 1.49; 95% confidence interval, 1.20-1.86); orofacial clefts (cleft lip without cleft palate: adjusted odds ratio, 1.41; 95% confidence interval, 1.10-1.81; cleft lip with or without cleft palate: adjusted odds ratio, 1.24; 95% confidence interval, 1.05-1.46; cleft palate alone: adjusted odds ratio, 1.31; 95% confidence interval, 1.06-1.63); bilateral renal agenesis (adjusted odds ratio, 1.99; 95% confidence interval, 1.05-3.75); amniotic band syndrome-limb body wall complex (adjusted odds ratio, 1.66; 95% confidence interval, 1.10-2.51); and atrial septal defects, secundum (adjusted odds ratio, 1.37; 95% confidence interval, 1.09-1.72). There were no significant inverse associations observed.
  
  
  CONCLUSIONS
  Additional studies replicating the findings are needed to better understand the moderate positive associations observed between periconceptional secondhand smoke and several birth defects in this analysis. Increased odds ratios resulting from chance (eg, multiple comparisons) or recall bias cannot be ruled out.
authors.affiliation: Birth Defects Epidemiology and Surveillance Branch, Texas Department of State Health Services, Austin, TX. Electronic address: adrienne.hoyt@dshs.state.tx.us.
authors.forename: Adrienne T
authors.initials: AT
authors.lastname: Hoyt
authors.affiliation: Birth Defects Epidemiology and Surveillance Branch, Texas Department of State Health Services, Austin, TX.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Canfield
authors.affiliation: Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, IA.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Romitti
authors.affiliation: Division of Medical Genetics, Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, UT.
authors.forename: Lorenzo D
authors.initials: LD
authors.lastname: Botto
authors.affiliation: Massachusetts Center for Birth Defects Research and Prevention, Massachusetts Department of Public Health, Boston, MA.
authors.forename: Marlene T
authors.initials: MT
authors.lastname: Anderka
authors.affiliation: Division of Medical Genetics, Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, UT.
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Krikov
authors.affiliation: Birth Defects Epidemiology and Surveillance Branch, Texas Department of State Health Services, Austin, TX.
authors.forename: Morgan K
authors.initials: MK
authors.lastname: Tarpey
authors.affiliation: Division of Medical Genetics, Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, UT.
authors.forename: Marcia L
authors.initials: ML
authors.lastname: Feldkamp
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D000013:Congenital Abnormalities / Q000209:etiology*; D005260:Female; D006306:Health Surveys; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D008297:Male; D018811:Maternal Exposure / Q000009:adverse effects* / Q000706:statistics & numerical data; D016017:Odds Ratio; D012307:Risk Factors; D014028:Tobacco Smoke Pollution / Q000009:adverse effects* / Q000706:statistics & numerical data; D014481:United States
chemical_list: D014028:Tobacco Smoke Pollution
keywords: birth defects; congenital defects; congenital heart defects; environmental tobacco smoke; malformations; passive smoking; secondhand smoke