title: Factors affecting thawed oocyte viability suggest a customized policy of embryo transfer.
abstract: OBJECTIVE
  To identify factors that might affect the clinical outcome of oocyte slow freezing.
  
  
  METHODS
  Retrospective study.
  
  
  METHODS
  Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
  
  
  METHODS
  Patients with spare metaphase II cryopreserved oocytes performing 371 thawing cycles.
  
  
  METHODS
  Oocytes were cryopreserved by slow freezing<40 hours after hCG administration (group A) and >or=40 hours after hCG administration (group B). Thawed oocytes were inseminated by intracytoplasmic sperm injection.
  
  
  METHODS
  Clinical pregnancy, implantation, abortion, and delivery rates.
  
  
  RESULTS
  Clinical pregnancy rate per thawed cycle (PR) and implantation rate (IR) were significantly higher in group A compared with group B both in young (PR: 25% vs. 9.6%; IR: 18.9% vs. 8.8%) and in older patients (PR: 25% vs. 10.1%; IR: 17.5% vs. 6.7%). In the young patient subgroup, clinical pregnancy and implantation rates with three transferred embryos were higher in group A vs. group B (PR: 72.7% vs. 25%, and IR: 36.4% vs. 12.5%, respectively). This difference was not found in the subgroup of older patients.
  
  
  CONCLUSIONS
  The timing at which oocyte cryopreservation is performed and the number of transferred embryos play a key role in the clinical outcome. The suggested cut-off time for cryopreservation is between 39 and 40 hours after hCG administration.
authors.affiliation: Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
authors.forename: Anna P
authors.initials: AP
authors.lastname: Ferraretti
authors.affiliation: Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Lappi
authors.affiliation: Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
authors.forename: M Cristina
authors.initials: MC
authors.lastname: Magli
authors.affiliation: Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Muzzonigro
authors.affiliation: Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Resta
authors.affiliation: Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy. Electronic address: luca.gianaroli@sismer.it.
authors.forename: Luca
authors.initials: L
authors.lastname: Gianaroli
mesh_terms: D000328:Adult; D002470:Cell Survival; D015925:Cryopreservation / Q000379:methods; D046149:Embryo Culture Techniques; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005615:Freezing / Q000009:adverse effects*; D006801:Humans; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D057285:Precision Medicine / Q000379:methods; D011247:Pregnancy; D018873:Pregnancy Rate; D027724:Reproductive Techniques, Assisted / Q000331:legislation & jurisprudence; D012189:Retrospective Studies; D012307:Risk Factors; D013696:Temperature