Factors affecting thawed oocyte viability suggest a customized policy of embryo transfer.
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.
Ferraretti
Anna P
AP
Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
Lappi
Michela
M
Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
Magli
M Cristina
MC
Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
Muzzonigro
Francesca
F
Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
Resta
Silvia
S
Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
Gianaroli
Luca
L
Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy. Electronic address: luca.gianaroli@sismer.it.
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