title: Association of twinning and maternal age with major structural birth defects in Utah, 1999 to 2008.
abstract: BACKGROUND
  Twinning is a risk factor for birth defects. Using population-based data from the Utah Birth Defect Network and the Utah Department of Health Vital Records, we investigated whether twinning increases the risk of major structural birth defects in live-born opposite-sex (OS) and same-sex (SS) twins as proxies for monozygotic and dizygotic twins, respectively. We also assessed whether maternal age modified the association between twinning and birth defects.
  
  
  METHODS
  All resident live-born singleton (n = 492,143) and twin (n = 13,596) infants issued a Utah birth certificate and delivered from 1999 through 2008 were included. Unadjusted and adjusted odds ratios (aORs) with 95% confidence intervals were calculated for each birth defect using unconditional logistic regression.
  
  
  RESULTS
  Birth defects were slightly more likely to occur in SS (aOR = 1.94; 95% confidence interval, 1.70-2.21) than OS (aOR = 1.55; 95% confidence interval, 1.27-1.90) twins. The aORs stratified by maternal age did not show a trend for any twin type when calculated for all birth defects combined. However, trends were observed for coarctation, pyloric stenosis, and shaft or penoscrotal hypospadias in OS twins; microcephaly, anotia/microtia, conotruncal defects, membranous ventricular septal defects, pyloric stenosis, all hypospadias, and craniosynostosis in SS twins; and tetralogy of Fallot, right ventricular outflow tract obstructions, renal agenesis/hypoplasia, and craniosynostosis in all twins.
  
  
  CONCLUSIONS
  All twin types have an increased risk for birth defects compared with singletons. SS twins have the highest risk, presumably due to the influence of monozygotic twins. The risk for birth defects in twins was not significantly modified by the mother's age.
authors.affiliation: Genomic Medicine Service, Department of Veterans Affairs, Salt Lake City, Utah 84148, USA. renee.rider@va.gov
authors.forename: Renee A
authors.initials: RA
authors.lastname: Rider
authors.forename: David A
authors.initials: DA
authors.lastname: Stevenson
authors.forename: Janice E
authors.initials: JE
authors.lastname: Rinsky
authors.forename: Marcia L
authors.initials: ML
authors.lastname: Feldkamp
mesh_terms: D000293:Adolescent; D000328:Adult; D000013:Congenital Abnormalities / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D012306:Risk; D012307:Risk Factors; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D014589:Utah / Q000453:epidemiology; D055815:Young Adult
keywords: birth defects; maternal age; population-based surveillance; twins