title: Prevalence of congenital heart defects in monochorionic/diamniotic twin gestations: a systematic literature review.
abstract: OBJECTIVE
  Congenital heart defects (CHDs) affect approximately 0.5% of all neonates. Recent literature points to a possible increase in the CHD prevalence among monochorionic/diamniotic (MC/DA) twin gestations. We hypothesized that MC/DA twin pregnancy is a risk factor for CHD.
  
  
  METHODS
  A systematic review of all published English literature was conducted on MEDLINE (Ovid and PubMed) from January 2000 through April 2007 using the medical subject heading terms "congenital heart defect" and "monozygotic twins." Four observational studies were included in the final analysis. Published historical data were used for the population background risk of CHD. Relative risk (RR) estimates with 95% confidence intervals (CIs) were calculated by fixed and random effect models.
  
  
  RESULTS
  We included a total of 40 fetuses with CHDs among 830 fetuses from MC/DA twin gestations. Compared with the population, CHDs were significantly more prevalent in MC/DA twins regardless of the presence of twin-twin transfusion syndrome (TTTS) (RR, 9.18; 95% CI, 5.51-15.29; P < .001). Monochorionic/diamniotic twin gestations affected by TTTS were more likely to be complicated by CHDs than those that did not have TTTS (RR, 2.78; 95% CI, 1.03-7.52; P = .04). Ventricular septal defects were the most frequent heart defects. Pulmonary stenosis and atrial septal defects were significantly more prevalent in pregnancies complicated with TTTS.
  
  
  CONCLUSIONS
  Monochorionic/diamniotic twin gestation appears to be a risk factor for CHDs. Conditions that lead to abnormal placentation may also contribute to abnormal heart development, especially in MC/DA twin pregnancies complicated with TTTS. Fetal echocardiography may be considered for all MC/DA twin gestations because ventricular septal defects and pulmonary stenosis are the most common defects.
authors.affiliation: Section of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology, and Reproductive Sciences, Yale University School of Medicine, New Haven, CT 06520, USA. mert.bahtiyar@yale.edu
authors.forename: Mert Ozan
authors.initials: MO
authors.lastname: Bahtiyar
authors.forename: Antonette T
authors.initials: AT
authors.lastname: Dulay
authors.forename: Bevin P
authors.initials: BP
authors.lastname: Weeks
authors.forename: Alan H
authors.initials: AH
authors.lastname: Friedman
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Copel
mesh_terms: D004200:Diseases in Twins / Q000453:epidemiology*; D005260:Female; D006330:Heart Defects, Congenital / Q000453:epidemiology*; D006801:Humans; D038622:Internationality; D011247:Pregnancy / Q000706:statistics & numerical data*; D015995:Prevalence; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic