RESUMEN
OBJECTIVE: We intended to know how the cryoprotectant ethylene glycol (EG) would affect the outcome of the embryo development when used in slow freezing method. And to know if there is any difference in the outcome of frozen-thawed embryos according to freezing methods and the timing. METHODS: We used 5-6 weeks old ICR female mice and T6 containing 0.4% BSA for basic culture media. The embryos at the developmental stages of 1-cell, 8-cell and blastocyst were cryopreserved respectively by slow freezing method using EG, propylene glycol (PROH), and glycerol as a cryoprotectant. We also compared the results of slow freezing and vitrification methods with the same cryoprotectant, EG. And finally, we evaluated the quality of blastocysts by counting the cell numbers in each group. RESULTS: The post-thaw embryo development were better in EG group when they were frozen at 1-cell and blastocyst stage (P<0.05). Although there were no differences in the recovery rate, the survival rate in vitrification group was significantly higher (P<0.05). Post-thaw embryo development to morula and blastocyst were better in vitrification group when frozen at 1-cell embryo (P<0.05), not at 8-cell and blastocyst group. The cell counts of blastocyst derived from 1-cell stage frozen EG group were significantly increased than that of PROH-glycerol groups (P<0.05), however, there was no difference between the two freezing methods. CONCLUSION: These results suggest that EG may be advantageous comparing with the conventional cryoprotectants, PROH and glycerol in slow freezing method for mouse embryo cryopreservation. In terms of freezing method, vitrification is better than slow freezing.