A prospective comparison of outcome following cryopreservation using vitrification vs. a modified slow-freeze protocol of 2 pronuclear (2PN) and day 3 multi-cell embryos

Abstract

Purpose: To compare the efficacy of vitrification of 2 pronuclear and day 3 cleavage stage embryo vs. a modified slow freeze protocol that historically has achieved good survival and pregnancy rates at these stages. Materials and Methods: Embryos were randomly assigned by day to freezing at the 2 proncular stage or day 3 cleavage stage embryos by either vitrification or a modified slow freeze protocol. Comparisons were made for survival rate, cleaveage rate, and pregnancy rate. Results: The results were comparable with a slight edge to vitrification. Only the implantation rates of day 3 cleavage staged embryos (75% vs. 30.4%) showed a significant difference. Conclusions: Vitrification seems to be equally or possibly slightly superior to freezing embryos at the 2 pronuclear or day 3 cleavage stage vs. a modified slow freeze protocol that had been previously found to be superior to the slow freeze method of LaSalle-Testart.