The Effect of Cryopreservation on the Mouse Embryos at Various-pronuclear Stages

This study was carried out to establish an appropriate condition for the efficient cryopreservation of the mouse pronuclear embryo. In vitro cryopreservation of pronuclear embryos was carried out by slow freezing or vitrification methods and development rate of 2-cell, blastocyst and hatched blastocyst was measured as well as survival rate of the thawed pronuclear embryo. After slow freezing, vitrification and thawing of mouse pronuclear embryos, the survival rate and blastocyst development rate for the vitrification group was 97.3 and 53.4%, respectively, which was significantly higher as compared to the slow freezing group with 88.6 and 23.9%, respectively (p<0.05). Blastocyst developmental rate in each experimental group was significantly higher for 21 h in the post-hCG group at 40.5-57.0% than the 24 h post-hCG group at 40.5% (p<0.05). ICM (Inner cell mass) cell numbers of blastocyst-stage embryos during the different stages of mouse pronuclear embryos, slow freezing and vitrification period in the control and vitrification groups were 22.1±2.7 and 17.0±3.1~22.0±3.2, respectively; hence, the slow freezing group (10.2±2.0) had significantly higher cell numbers than those of the other two groups (p<0.05). Trophoblast (TE) cell number in the control group, 65.8±12.6, was significantly higher than in the slow freezing group, 41.6±11.1 (p<0.05). The total cell numbers in the control group and 21 h post hCG group were 87.9±13.6 and 81.8±14.1, respectively, and were significantly higher than for the slow freezing group (51.8±12.6; p<0.05). (