ABSTRACT
Objective: To compare the efficiency of two cryopreservations between conventional slow freezing and vitrification of mouse blastocysts using cryo-E. Methods: ICR female mice (8 weeks) were superovulated with 5 IU/ml of pregnant mare serum gonadotrophin (PMSG), the successfulness of mating with males was verified by the presence of a vaginal plug. Blastocysts were obtained between 3.5 and 4.5 days per p.c. or 96-108 hours after hCG administration by flushing the uterus. Randomly selected blastocysts were simultaneously frozen by slow-rate freezing and a vitrification method. One month later, the embryos were thawed and cultured in the blastocyst medium (COOK; Sydney IVF, Australia). Results: Based on 250 slow freezing and 310 vitrified mouse blastocysts, vitrification resulted in a slightly higher survival and hatching rates than the slow-freezing method (83.9% VS 82.0%, and 68.8% VS 66.8%, respectively). Conclusion: Both slow freezing and vitrification of mouse blastocysts are useful methods for cryopreservation. These results showed that vitrification is better than slow freezing in terms of simplicity, duration, and cost-effectiveness.