EFFECTS OF COOLING AND EQUILIBRATION IN DMSO, AND CRYOPRESERVATION OFMOUSE OOCYTES, ON THE RATES OF IN-VITRO FERTILIZATION, DEVELOPMENT, AND CHROMOSOMAL-ABNORMALITIES

In a previous study, we have shown that the cryopreservation of mouse oocytes caused increases in the rates of degeneration and of digynic p olyploid embryos, while the fertility of frozen-thawed oocytes was dec reased. In this study, we have attempted to determine the different st ages in the complete freezing-thawing process which are deleterious fo r the oocytes and the subsequent zygotes. IVF assays showed that DMSO decreased the fertility of oocytes, whereas cooling to 0 degrees C had no effect. DMSO, used at 0 degrees C, was less deleterious for oocyte s. Thus, the prefreezing manipulations seem to be important for the qu ality and fertility of oocytes. However, neither DMSO nor cooling incr eased the incidence of chromosomal abnormalities in embryos obtained f rom inseminated exposed oocytes. Therefore, the increased frequency of polyploidy observed in embryos after the cryopreservation of mouse oo cytes must correspond to disruption occurring during the freezing-thaw ing process. (C) 1995 Wiley-Liss, Inc.