title: Antenatal sonographic prediction of twin chorionicity.
abstract: OBJECTIVE
  We sought to determine the accuracy of antenatal diagnosis of twin chorionicity at a single tertiary care center and assess the consequences of incorrect diagnoses.
  
  
  METHODS
  Twins with chorionicity diagnosed by ultrasound < or = 24 weeks' gestation were retrospectively reviewed. Chorionicity was assigned by sonographic findings including placental location(s), the lambda and T-signs, and/or fetal gender(s). Postnatal diagnosis was determined by placental histopathologic examination. Medical records of antenatal-postnatal discordant chorionicities were reviewed for adverse sequelae.
  
  
  RESULTS
  Chorionicity was correctly assigned antenatally in 392/410 (95.6%) twins. The sensitivity, specificity, and positive and negative predictive values of monochorionicity assessed < or = 14 weeks were 89.8%, 99.5%, 97.8%, and 97.5%. Corresponding statistical values for the second trimester were 88.0%, 94.7%, 88.0%, and 94.7%. Two cases of inaccurate antenatal diagnoses affected patient counseling or were associated with adverse clinical outcomes.
  
  
  CONCLUSIONS
  Antenatal assessment of chorionicity is accurate; however, incorrect diagnoses do occur and can affect reliable patient counseling and management.
authors.affiliation: Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Columbia University Medical Center, New York, NY 10032, USA. yml2102@columbia.edu
authors.forename: Young Mi
authors.initials: YM
authors.lastname: Lee
authors.forename: Jane
authors.initials: J
authors.lastname: Cleary-Goldman
authors.forename: Harshwardhan M
authors.initials: HM
authors.lastname: Thaker
authors.forename: Lynn L
authors.initials: LL
authors.lastname: Simpson
mesh_terms: D002823:Chorion / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D005260:Female; D005865:Gestational Age; D006801:Humans; D010920:Placenta / Q000002:abnormalities / Q000473:pathology; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D011272:Pregnancy, Multiple; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014427:Twins; D016216:Ultrasonography, Prenatal