title: Comparison of modes of ascertainment for mosaic vs complete trisomy 21.
abstract: OBJECTIVE
  We sought to compare the indications for amniocentesis leading to the detection of either mosaicism of trisomy 21 (mosaic-T21) or complete trisomy 21 (T21).
  
  
  METHODS
  A retrospective review of a large amniocentesis database (n = 494,163) was conducted. All specimens with mosaic-T21 (n = 124) were compared with a maternal age-matched group of T21 fetuses (n = 496). Samples with normal karyotypes were matched for maternal age and served as normal controls (n = 496). The chi(2) testing was used for statistical analysis.
  
  
  RESULTS
  The presence of an abnormal first-trimester screen, abnormal sonographic findings, and specifically the single sonographic abnormalities of either a cystic hygroma or a cardiac anomaly were significantly less common in the mosaic-T21 as compared with the T21 group. There were no such differences between the mosaic-T21 and the normal control group.
  
  
  CONCLUSIONS
  Fetuses with mosaic-T21, similar to those with normal karyotype, do not present with the same abnormal screening tests as fetuses with T21.
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, New York University School of Medicine, New York, NY, USA.
authors.forename: Eran
authors.initials: E
authors.lastname: Bornstein
authors.forename: Erez
authors.initials: E
authors.lastname: Lenchner
authors.forename: Alan
authors.initials: A
authors.lastname: Donnenfeld
authors.forename: Sara
authors.initials: S
authors.lastname: Kapp
authors.forename: Sean M
authors.initials: SM
authors.lastname: Keeler
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Divon