P-30: Developmental Capacity and Blastocyst Formation of Thawed Tetrahedral Versus Non-Tetrahedral 4-cell Stage Mouse Embryos After Vitrification

Background: It was reported in a literature that approximately one third of the 4-cell stage embryos did not exhibit a tetrahedral shape. Non-tetrahedral embryos showed a lower in vitro developmental potential than tetrahedral embryos. Recently vitrification technology has been widely employed for embryo cryopreservation. The objective of this study was to prove our hypothesis that vitrified - thawed tetrahedral embryos have the higher probabilities to blastocyst formation versus non-tetrahedral 4-cell stage embryos. Materials and Methods: Female mice (NMRI, 8-10 weeks-old) were stimulated with 5 IU pregnant mare&#039;s serum gonadotropin followed 48 hours later with 5 IU human chorionic gonadotropin (HCG). And animals were caged with one male mouse for mating. Mated mice were killed by cervical dislocation to collect zygotes from oviduct of pregnant 2 d mice. The architecture of 4-cell embryos of 20 mice was evaluated and divided for two tetrahedral and non- tetrahedral groups. Four cell embryos were vitrified with cryotip using the Vitrification solution including of 15%EG, 15%DMSO and 0, 5 M sucrose and were stored in liquid nitrogen for a period of 8-10 days. Five 4-cell zygotes were placed on each cryotip. After warming, embryos were cultured in T6 medium and the rates of embryo cryo-survival, cleavage and embryo development to the blastocyst stage were compared. The results were analyzed by student t test. Results: Of the 223 four-cell embryos evaluated on day 2, 145 (65%) had a tetrahedral shape and 78(35%) did not. Survival rate after thawing in 145 tetrahedral thawed embryos was 94 %. Similar results concerning the survival rates of the 4-cell embryos after thawing for non tetrahedral shape group (89%) could be seen. Tetrahedral group had the highest (p<0.05) cleavage and formation of blastocyst stage embryos rate in comparison to non-tetrahedral group. Conclusion: There was no significant difference in embryos cryo-survival rates among the two groups examined. However, the rates of embryos developed to blastocyst stage in the non-tetrahedral group were reduced significantly compared with the tetrahedral group.