Related Experiment Video
Updated: Jun 21, 2026
Fertility Preservation Through Oocyte Vitrification: Clinical and Laboratory Perspectives
Published on: September 16, 2021
Factors affecting thawed oocyte viability suggest a customized policy of embryo transfer
Anna P Ferraretti1, Michela Lappi1, M Cristina Magli1
1Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
Objective:
To identify factors that might affect the clinical outcome of oocyte slow freezing.
Design:
Retrospective study.
Setting:
Reproductive Medicine Unit, Italian Society for the Study of Reproductive Medicine, Bologna, Italy.
Patient(S):
Patients with spare metaphase II cryopreserved oocytes performing 371 thawing cycles.
Intervention(S):
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.
Main Outcome Measure(S):
Clinical pregnancy, implantation, abortion, and delivery rates.
Result(S):
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.
Conclusion(S):
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.
