Normal survival and in-vitro development after cryopreservation of zona-drilled embryos in mice.

The importance of the zona pellucida on survival after freezing and thawing was investigated. Zona-drilled and zona-intact mouse embryos were fertilized in vitro, cultured to the 2, 4 and 8-cell stages and frozen using conventional methods. Zona drilling did not affect the survival or development of frozen embryos to the blastocyst stage in vitro. We conclude that partial damage to the zona pellucida during micromanipulation procedures is compatible with rates of survival and development which are not different to those observed in zona-intact control embryos.