Development and hatching of the blastocyst

During early embryonic development, the embryo is surrounded by a protein layer that protects it: the zona pellucida. As the embryo grows and increases in size, the zona pellucida thins until the expanded blastocyst breaks free of it, a phenomenon known as hatching.

Depending on the day of development, the state of the zona pellucida, and the appearance of the embryo, we can differentiate between: compact blastocyst, expanded blastocyst, hatching blastocyst, and hatching blastocyst.