Zona hatching is a phenomenon occurring during prenatal development. Prior to this event, the predecessor of the embryo, in the form of a blastocyst

Blastocyst

The blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula. It is a specifically mammalian example of a blastula. It possesses an inner cell mass , or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast,...

, is surrounded by a glycoprotein sphere called the zona pellucida

Zona pellucida

The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but of essential importance to it...

. To be able to perform implantation on the uterine

Uterine

The word uterine can refer to different meanings:* relating to or near the uterus or womb* having the same mother, but different fathers, see matrilineality...

 wall, the blastocyst first needs to get rid of the zona pellucida. This lysis of the zona pellucida is called the zona hatching.

Uses of the term

In some situations, the term "hatching" is used only for artificial ways to free the blastocyst from the zona pellucida, and not the natural lysis of it. An example of such artificial way is Assisted zona hatching

Assisted zona hatching

Assisted zona hatching is a procedure of assisted reproductive technology in which a small hole is made in the zona pellucida, using a micromanipulation, thereby facilitating for zona hatching to occur.....

.