title: Chromosomal mosaicism throughout human preimplantation development in vitro: incidence, type, and relevance to embryo outcome.
abstract: BACKGROUND
  A large percentage of in-vitro generated cleavage stage human embryos are chromosomally mosaic, consisting of both normal (diploid) and abnormal (non-diploid) cells. The present study characterized mosaicism at each stage of cleavage division and examined its effect on preimplantation development in vitro.
  
  
  METHODS
  A total of 216 normally fertilized (two-pronucleate) embryos which were not selected for transfer to the patients were analysed for chromosomal abnormalities using multi-colour fluorescence in-situ hybridization DNA probes specific for three to five of nine different chromosomes (X, Y, 2, 7, 13, 16, 18, 21, 22).
  
  
  RESULTS
  Overall, 48.1% of embryos were mosaic. The frequency of mosaic embryos increased from 15.2 to 49.4 to 58.1%, from the 2-4-cell to 5-8-cell to morula stages respectively, and the types of non-diploid cells detected were mostly aneuploid or chaotic. The incidence of mosaicism at the blastocyst stage was 90.9%; however, most of the mosaicism comprised diploid and polyploid cells. Arrested mosaic embryos had a higher incidence of chaotic abnormalities, and higher proportions of abnormal cells compared with the non-arrested group.
  
  
  CONCLUSIONS
  Post-zygotic errors leading to mosaicism may occur, and persist throughout preimplantation development in vitro. Our results suggest that mosaicism involving multiple chromosomal imbalances and/or imbalances affecting a high proportion of cells in an embryo appear to impair development to the blastocyst stage.
authors.affiliation: Departments of Obstetrics and Gynecology, Royal Victoria Hospital, McGill University, Montreal, QC H3A 1A1, Canada.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Bielanska
authors.forename: Seang Lin
authors.initials: SL
authors.lastname: Tan
authors.forename: Asangla
authors.initials: A
authors.lastname: Ao
mesh_terms: D000328:Adult; D000782:Aneuploidy; D001755:Blastocyst; D002875:Chromosomes / Q000235:genetics*; D005314:Embryonic and Fetal Development; D005260:Female; D005787:Gene Frequency; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D009030:Mosaicism; D011247:Pregnancy; D011256:Pregnancy Outcome