This document summarizes the results of a clinical audit comparing outcomes of 706 embryos that were either vitrified or slow-frozen for fertility treatment. The audit found statistically significant improvements in survival rate, pregnancy rate per embryo thawed, clinical pregnancy rate per embryo thawed, and implantation rate per embryo thawed for embryos that were vitrified compared to those that were slow-frozen after adjusting for patient age differences between the groups. The conclusion is that vitrification led to highly significant improvements in all outcome measures compared to slow-freezing based on this retrospective analysis of data.