title: Vitrification of human blastocysts previously cryopreserved by slow controlled-rate freezing at the cleavage stage.
abstract: OBJECTIVE
  The objective of this study was to evaluate the efficiency of vitrified blastocysts derived from frozen-thawed cleavage stage embryos in terms of morphological survival and re-expansion status of the blastocoelic cavity.
  
  
  RESULTS
  After warming 162 blastocysts derived from fresh embryos (= control group) and 90 blastocysts from frozen-thawed cleavage stage embryos (= study group) and after 2-3 h of in vitro culture the percentage of blastocysts with morphological survival was not different between the two groups. After 24 h of in vitro culture, the percentage of fully expanded, hatching or hatched blastocysts was not different between both groups.
  
  
  CONCLUSIONS
  The results show that blastocysts derived from frozen-thawed cleavage stage embryos can be cryopreserved successfully a second time by vitrification method. Re-cryopreservation by vitrification still needs to be approached with some caution because little data on long term safety of multiple freezing is available.
authors.affiliation: Department for Reproductive Medicine, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium, sylvie.lierman@ugent.be.
authors.forename: S
authors.initials: S
authors.lastname: Lierman
authors.forename: E
authors.initials: E
authors.lastname: Van den Abbeel
authors.forename: P
authors.initials: P
authors.lastname: De Sutter
mesh_terms: D001755:Blastocyst / Q000166:cytology*; D015925:Cryopreservation / Q000379:methods*; D046149:Embryo Culture Techniques; D004622:Embryo, Mammalian; D047108:Embryonic Development; D006801:Humans; D058989:Vitrification