Ultrastructural studies of frozen-thawed 8-cell mouse embryos.

Survival of frozen 8-cell mouse embryos transferred directly upon thawing to the uteri of Day 3 pseudopregnant foster mothers was significantly lower (26%) than the survival of unfrozen 8-cell embryos transferred immediately after collection (73%). When frozen-thawed 8-cell embryos were cultured for 20-24 hr before transfer survival was similar to that of unfrozen 8-cell embryos transferred after 20-24 hr inculture (65% and 73%, respectively). Ultrastructural examination of the frozen-thawed 8-cell embryos revealed no obvious damage to protoplasmic components.