Blastocyst expansion rates

Depending on its expansion, the blastocyst can be classified as early, cavitated, expanded, initiating hatching, or hatching. The early blastocyst is one that is beginning to cavitate, that is, the blastocele begins to form to give rise to the complete blastocyst structure. When it is cavitated, the blastocele has already formed, but it must continue to fill with fluid so that the blastocyst can expand. When it is expanded, the blastocyst is larger and the zona pellucida is thinner, so hatching can begin, i.e. the exit of the zona pellucida. Once it has hatched, implantation can take place.