title: Prospective randomized comparison of human oocyte cryopreservation with slow-rate freezing or vitrification.
abstract: OBJECTIVE
  To compare cryopreservation of mature human oocytes with slow-rate freezing and vitrification and determine which is most efficient at establishing a pregnancy.
  
  
  METHODS
  Prospective randomized.
  
  
  METHODS
  Academically affiliated, private fertility center.
  
  
  METHODS
  Consenting patients with concerns about embryo cryopreservation and more than nine mature oocytes at retrieval were randomized to slow-rate freezing or vitrification of supernumerary (more than nine) oocytes.
  
  
  METHODS
  Oocytes were frozen or vitrified, and upon request oocytes were thawed or warmed, respectively.
  
  
  METHODS
  Oocyte survival, fertilization, embryo development, and clinical pregnancy.
  
  
  RESULTS
  Patient use has resulted in 30 thaws and 48 warmings. Women's age at time of cryopreservation was similar. Oocyte survival was significantly higher following vitrification/warming (81%) compared with freezing/thawing (67%). Fertilization was more successful in oocytes vitrified/warmed compared with frozen/thawed. Fertilized oocytes from vitrification/warming had significantly better cleavage rates (84%) compared with freezing/thawing (71%) and resulted in embryos with significantly better morphology. Although similar numbers of embryos were transferred, embryos resulting from vitrified oocytes had significantly enhanced clinical (38%) pregnancy rates compared with embryos resulting from frozen oocyte (13%). Miscarriage and/or spontaneous abortion rates were similar.
  
  
  CONCLUSIONS
  Our results suggest that vitrification/warming is currently the most efficient means of oocyte cryopreservation in relation to subsequent success in establishing pregnancy.
authors.affiliation: Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: Gary D
authors.initials: GD
authors.lastname: Smith
authors.forename: Paulo C
authors.initials: PC
authors.lastname: Serafini
authors.forename: Joyce
authors.initials: J
authors.lastname: Fioravanti
authors.forename: Isaac
authors.initials: I
authors.lastname: Yadid
authors.forename: Marcio
authors.initials: M
authors.lastname: Coslovsky
authors.forename: Pericles
authors.initials: P
authors.lastname: Hassun
authors.forename: José Roberto
authors.initials: JR
authors.lastname: Alegretti
authors.forename: Eduardo L
authors.initials: EL
authors.lastname: Motta
mesh_terms: D000328:Adult; D015925:Cryopreservation / Q000379:methods*; D004624:Embryo Transfer / Q000379:methods; D005260:Female; D005306:Fertilization / Q000502:physiology; D005615:Freezing; D006801:Humans; D009865:Oocytes; D010062:Ovulation Induction / Q000379:methods; D011247:Pregnancy; D018873:Pregnancy Rate; D020554:Sperm Injections, Intracytoplasmic / Q000379:methods; D013997:Time Factors