The zona pellucida is the shell or outer layer that covers the oocyte. It has several functions:
Prevent more than one sperm from entering at the time of fertilization
Avoid pre-mature separation when the embryo has a few cells
Prevent the embryo from implanting prematurely
All functions are essential, but by the fifth day after fertilization, the embryo needs to leave this shell and hatch. Sometimes this process fails.
This technique helps to get better results of IVF. It consists on perforating the zona pellucida to facilitate its hatch and subsequent implantation.
This practice is recommended for patients with advanced reproductive age, in patients who´s oocyte have a thick zona pellucida and for all embryos before a cryopreservation transfer.