A comparison of starting temperatures for slow freezing cryopreservation of blastocysts

Abstract

OBJECTIVE: To compare starting temperature of 20 degrees C with -6.5 degrees C utilizing slow freezing and Menezo two step protocols for blastocyst cryopreservation by evaluating the resulting implantation rate at the time of thaw and transfer for each group. DESIGN: Retrospective study conducted in a University IVF program. MATERIALS AND METHODS: All patients between August 2006 and October 2007 with cryopreservation were randomized and included in this study. Data was analyzed on 258 blastocyts from 143 patients that were cryopreserved using Sage Blastocyst Freezing Media (RM-ART-8016). 146 blastocysts were cryopreserved using -6.5 degrees C as the starting temperature and 111 blastocysts were cyropreserved using 20 degrees C as the starting temperature. Thawing was performed using the two step Sage thaw protocol (RM-ART-8015). Survival and re-expansion were graded prior to transfer. The % survival is equal to the number of live cells. The % re-expansion reflects the size of the blastocele cavity. RESULTS: Using minitab anova one-way analysis, the following results were found: There was no significant difference in the number of embryos transferred, time in culture, % re-expansion or implantation rate. There was a significant difference between the two groups in average patient age, with the -6.5 degree C group exhibiting an older population. Interestingly, this same group exhibited higher % survival, but this was not significant. CONCLUSIONS: Changing the starting temperature to -6.5 degrees C for slow freezing of blastocyst did not impact implantation rate in patients and actually lead to a better survival rate, although not significant, in the slightly older group of patients. Blastocyst survival and re-expansion were not affected by the change in starting temperature. The change to -6.5 degrees C for slow freezing shortens the time necessary to complete this process saving personnel time without sacrificing frozen embryo quality.Table 1Starting Temp.no. embryosaverage patient ageaverage no. EThours in culture-6.5 degrees C14636.021.983.0120 degrees C11134.172.092.74P<0.010.2180.030 Open table in a new tab Table 2Starting Temp.% survival% re-expansionIR-6.5 degrees C88.2737.970.2120 degrees C80.6233.170.16P<0.010.3060.241 Open table in a new tab