title: Comprehensive molecular cytogenetic analysis of the human blastocyst stage.
abstract: BACKGROUND
  The high frequency of chromosomal abnormalities observed in human gametes and embryos is unlike that seen in other mammalian species and is of great clinical significance, leading to high rates of pregnancy loss, and live-born children with aneuploid syndromes. Although much is known concerning the aneuploidy rates of oocytes, cleavage stage embryos and fetuses during pregnancy, the chromosomal status of blastocysts has been relatively little investigated.
  
  
  METHODS
  A total of 158 good quality blastocysts were examined using micromanipulation, whole genome amplification and comparative genomic hybridization.
  
  
  RESULTS
  From the obtained data, it was evident that the aneuploidy rate (38.8%) is significantly lower for blastocysts than for embryos at earlier stages (51%). However, in many cases, chromosome errors, including monosomy, imbalance affecting the larger chromosomes and complex aneuploidy persisted to this final stage of preimplantation development.
  
  
  CONCLUSIONS
  This study represents the first attempt to gain a detailed insight into the extent and type of chromosome errors seen at the blastocyst stage, using a comprehensive molecular cytogenetic method. Our data suggest that the blastocyst stage does not represent an absolute selective barrier, and that the majority of aneuploid embryos are lost at the time of implantation or shortly thereafter.
authors.affiliation: Nuffield Department of Obstetrics and Gynaecology, University of Oxford, Oxford, UK. elpida.fragouli@obs-gyn.ox.ac.uk
authors.forename: E
authors.initials: E
authors.lastname: Fragouli
authors.forename: M
authors.initials: M
authors.lastname: Lenzi
authors.forename: R
authors.initials: R
authors.lastname: Ross
authors.forename: M
authors.initials: M
authors.lastname: Katz-Jaffe
authors.forename: W B
authors.initials: WB
authors.lastname: Schoolcraft
authors.forename: D
authors.initials: D
authors.lastname: Wells
mesh_terms: D000328:Adult; D000782:Aneuploidy; D001755:Blastocyst / Q000166:cytology*; D002875:Chromosomes / Q000648:ultrastructure; D003582:Cytogenetics; D004624:Embryo Transfer; D005260:Female; D005821:Genetic Techniques; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008875:Middle Aged; D009693:Nucleic Acid Hybridization; D010062:Ovulation Induction; D019836:Preimplantation Diagnosis