title: Comparison of vitrification and conventional cryopreservation of day 5 and day 6 blastocysts during clinical application.
abstract: OBJECTIVE
  To evaluate implantation of day 5 and day 6 vitrified and slow-frozen blastocysts.
  
  
  METHODS
  Retrospective analysis comparing two cryopreservation techniques.
  
  
  METHODS
  Private IVF clinic.
  
  
  METHODS
  Five hundred eight cryopreserved embryo transfer candidates.
  
  
  METHODS
  Supernumerary day 5 and day 6 blastocysts were vitrified or slow-frozen and transfered after warming or thawing.
  
  
  METHODS
  Comparison of two cryopreservation techniques with respect to survival rate, implantation, and pregnancy rates of day 5 and day 6 blastocysts.
  
  
  RESULTS
  In 254 vitrified transfer cycles, survival, embryonic implantation, and clinical pregnancy rates for day 5 blastocysts were 95.9%, 33.4%, 48.7%, respectively, and for day 6 blastocysts 97.5%, 25.9%, 42.8%. In 254 slow-frozen transfer cycles, survival, embryonic implantation, and clinical pregnancy rates for day 5 blastocysts were 91.4%, 29.6%, 42.8%, respectively, and for day 6 blastocysts 94.8%, 28.2%, 43.1%. Overall there was a slightly, but not significantly, higher outcome regarding implantation and clinical pregnancy with the use of day 5 blastocysts (31.3% and 45.4%, respectively) versus day 6 blastocysts (26.7, and 42.9%, respectively).
  
  
  CONCLUSIONS
  Vitrification technique yields the same implantation and pregnancy rate as slow-frozen blastocyst transfers. Slow growing embryos can be cryopreserved on day 6, because they yield a satisfactory survival, implantation, and pregnancy rate.
authors.affiliation: Fertility Centers of Illinois, Chicago, Illinois 60610, USA. juergen.liebermann@integramed.com
authors.forename: Juergen
authors.initials: J
authors.lastname: Liebermann
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Tucker
mesh_terms: D000328:Adult; D001755:Blastocyst / Q000166:cytology* / Q000502:physiology; D002470:Cell Survival; D015925:Cryopreservation / Q000379:methods* / Q000706:statistics & numerical data*; D004624:Embryo Transfer / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007247:Infertility, Female / Q000453:epidemiology* / Q000473:pathology / Q000628:therapy*; D011247:Pregnancy; D018873:Pregnancy Rate; D016896:Treatment Outcome; D014481:United States