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.

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.