title: Molecular zygosity studies aid in the management of discordant multiple gestations.
abstract: OBJECTIVE
  Management of multiple gestations often requires identification of chorionicity. Sonographic evidence of dichorionicity can be present or inconclusive. DNA determination of zygosity can aid in the subsequent management of twins who are discordant for growth or anomalies.
  
  
  METHODS
  We present four cases in which monochorionicity could not be excluded sonographically. DNA zygosity studies were performed on amniocytes to guide management of the pregnancies.
  
  
  RESULTS
  In two cases, one twin was affected with a significant anomaly. DNA zygosity studies provided a greater than 99% likelihood of monozygous twins in both cases. This altered the counseling regarding selective termination options. The other two cases involved severe intrauterine growth restriction and oligohydramnios in one twin, with a normal co-twin. The small twin appeared nonviable, and DNA studies were used to assess risk to the normal twin in the event of the co-twin's demise. We recommended delivery in the event of monozygous twinning and expectant management if the twins were dizygous.
  
  
  CONCLUSIONS
  Diagnosis of chorionicity is important in multiple gestations. When chorionicity is unclear and management decisions would be altered by determination of zygosity, DNA studies should be considered.
authors.affiliation: Department of Obstetrics, Gynecology, and Reproductive Biology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Norton
authors.forename: M E
authors.initials: ME
authors.lastname: D'Alton
authors.forename: D W
authors.initials: DW
authors.lastname: Bianchi
mesh_terms: D000025:Abortion, Eugenic; D000328:Adult; D000650:Amnion / Q000166:cytology; D000013:Congenital Abnormalities / Q000175:diagnosis* / Q000235:genetics; D004247:DNA / Q000032:analysis*; D004200:Diseases in Twins; D005260:Female; D005313:Fetal Death / Q000235:genetics; D005315:Fetal Diseases / Q000175:diagnosis; D006801:Humans; D007231:Infant, Newborn; D007621:Karyotyping; D008297:Male; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011272:Pregnancy, Multiple; D011296:Prenatal Diagnosis; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics*
chemical_list: D004247:DNA