Assessment of the developmental potential of frozen-thawed mouse oocytes

Abstract

Mouse oocytes were cryopreserved by a protocol shown previouslyto minimize damage tot the zona peelucida and cytoskeletal system. After thawing, the incidence of fertilization didnot differ from that in control groups of oocytes, and after fertilizaiton, the ability of the fertilized frozen–thawed oocytes to develop tothe balstocyst stage in vitro was only slightly less (77%) than that of the controls (87 and 89%). Transfer of frozen–thawed and fertilized oocytes after their culture to the balstocyst stage in vitro resulted in a lower implantation rate (46%) than for the controls (68–73%), but of the implanting embryos the same proportions in experimental and control groups survived toyield vaiable fetuses. In contrast, transfer after culture in vitro to the 2-to 4-cell stage rsulted in similar implantation rates for control and frozen–thawed fertilized oocytes (70–84%), but the spontaneous abortion rate was higher for the embryos derived from frozen–thawed oocytes. Overall the cumulative survival rate for frozen oocytes transferrd at the 2-cell stage (36%) was better than after transfer at the blastocyst stage (30%), but both were less than for the transfer at any stage of the control oocytes (47–55%). The cumulative survival of cryopreserved oocytes to viable fetuses was 30–40% less than that of the control oocytes. These results are compared with those form previous studies and the main remaining obstacles to completely successful cryopreservation are identified