A SIMPLE RAPID 4.5-M DIMETHYLSULFOXIDE FREEZING TECHNIQUE FOR THE CRYOPRESERVATION OF ONE-CELL TO BLASTOCYST STAGE PREIMPLANTATION MOUSE EMBRYOS

This study applies a 4.5 M dimethyl-sulfoxide freezing procedure, developed for 2-cell mouse embryos, to pronuclear to hatched blastocyst stage mouse embryos. The embryos were plunged into liquid nitrogen after 3 min equilibration at room temperature, or 3-60 min equilibration at 0-degrees-C. Equilibration at 0-degrees-C gave survival rates as high as or higher than rates after equilibration at room temperature. Optimal blastocyst formation, or re-expansion, rates for embryos frozen after equilibration at 0-degrees-C were 76% for pronuclear stage embryos and 96-100% for 2-cell to mid-blastocyst stage embryos. The optimal rates of fetus formation, per embryo frozen, ranged from 62 to 88% for pronuclear to mid-blastocyst stage embryos. These results compared favourably with non-frozen control embryos (80-100% blastocyst formation, and 67-78% fetus formation).