Cryopreservation and transfer of baboon embryos.

The feasibility of modifying bovine cryopreservation methods for use with baboon embryos was evaluated. Twenty-six baboon embryos at the eight-cell to blastocyst stage of development were transferred after being frozen using glycerol as cryoprotectant. Either a two-step fast of a controlled linear temperature depression was achieved to -40 degrees C, followed by plunging into liquid nitrogen. After thawing, embryos were rehydrated in medium containing sucrose (0.5 to 1.0 M) using various methods of glycerol dilution. Embryos were transferred nonsurgically to anesthetized recipient baboons. Two term pregnancies resulted from six embryos frozen using the controlled linear cooling method and rehydrated by dropwise dilution of the sucrose (0.8 M) medium. Later cell stages had a greater morphological integrity postthaw than did earlier developmental stages, and embryos frozen by the linear cooling-rate method had less cell damage than those frozen by the fast method.