AN INTACT ZONA-PELLUCIDA IS NOT NECESSARY FOR SUCCESSFUL MOUSE EMBRYO CRYOPRESERVATION

Objective: To determine the developmental potential of mouse embryos that underwent cryopreservation after micromanipulation of the zona pellucida. Design: Gaps were produced in the zona pellucida of mouse oocytes or two-cell embryos by zona drilling with acid Tyrode's solution. Zona-drilled oocytes were fertilized in vitro and cultured to the two-cell stage. Two-cell embryos were frozen, thawed, and cultured to the expanded blastocyst stage. Results: There was no difference in the rate of embryo survival post-thaw (248/318, 77% versus 288/345, 83.4%), or in the rate of development to the expanded blastocyst stage (91/248, 36.7% versus 88/288, 30.6%), between embryos that were zona drilled as oocytes and unmanipulated controls. Similarly, there was no difference in the rate of cryosurvival (206/217, 94.9% versus 168/187, 89.8%) or development to the blastocyst stage (154/206, 74.7% versus 132/168, 78.6%) between embryos that were fertilized in vivo and zona drilled at the two-cell stage and embryos that were unmanipulated. Conclusions: These findings indicate that small gaps in the zona pellucida, such as those that result from micromanipulation, do not significantly alter the ability of embryos to withstand cryopreservation.