title: Elevated incidence of chromosomally chaotic embryos among frozen-thawed preimplantation embryos.
abstract: OBJECTIVE
  The aim of the study was to evaluate the effect of cryopreservation on the formation of chromosomal abnormalities in human preimplantation embryos.
  
  
  METHODS
  The chromosomal constitutions of cleavage stage embryos (n = 61) were assessed using fluorescent in situ hybridisation (FISH) technique, applying probes for chromosomes 13, 16, 18, 21, X and Y. Study group embryos frozen at zygote or two-cell stage (n = 29) were cultured in vitro post-thawing until they reached four- to six-cell stage, after which their chromosomal constitutions were assessed. Control group embryos frozen at four- to six-cell stage (n = 32) were analysed immediately after thawing in order to exclude any post-thaw effect. The proportions of genetically normal and abnormal embryos were compared between study and control group.
  
  
  RESULTS
  The proportions of normal, aneuploid and mosaic embryos were similar in both groups. However, significantly (P < 0.05) higher proportion of chaotic embryos in study (24.1%) compared to control group (6.3%) was observed.
  
  
  CONCLUSIONS
  The elevated level of chromosomally chaotic embryos among embryos that had undergone cellular division after thawing as compared to embryos analysed immediately after thawing indicates a potential negative impact of cryopreservation on the formation of chromosomal abnormalities in preimplantation embryos.
authors.affiliation: Infertility Clinic, The Family Federation of Finland, Helsinki, Finland. andres.salumets@vaestoliitto.fi
authors.forename: Andres
authors.initials: A
authors.lastname: Salumets
authors.forename: Nina
authors.initials: N
authors.lastname: Horelli-Kuitunen
authors.forename: Anne-Maria
authors.initials: AM
authors.lastname: Suikkari
authors.forename: Andres
authors.initials: A
authors.lastname: Metspalu
authors.forename: Timo
authors.initials: T
authors.lastname: Tuuri
mesh_terms: D000328:Adult; D001755:Blastocyst / Q000473:pathology*; D016022:Case-Control Studies; D002869:Chromosome Aberrations; D015925:Cryopreservation; D047108:Embryonic Development / Q000235:genetics*; D005260:Female; D005307:Fertilization in Vitro; D005387:Finland / Q000453:epidemiology; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D015994:Incidence; D011247:Pregnancy