Determining the most optimal stage for embryo cryopreservation.

The objective of this study was to compare cleaved embryo and blastocyst freezing to determine the optimal time for embryo cryopreservation. A retrospective analysis was carried out for all frozen embryo transfer cycles where transfer occurred on either day 3 or day 5. Blastocyst freezing increased the ongoing pregnancy, implantation and survival rates post-thaw as compared with cleaved embryo thaws. There was no difference in ongoing pregnancies for fresh and frozen-thawed blastocyst transfers (59% versus 62%) respectively. Additionally, fresh blastocyst transfers had a higher proportion of supernumerary embryos cryopreserved than did day 3 transfers (38% versus 26%). Blastocyst freezing is a viable option for handling patient's supernumerary embryos while optimizing pregnancy outcomes per oocyte retrieval.