Assisted Hatching

Assisted hatching (AH) is a micromanipulation technique in which the laser beam (the most safe way in AH) creates a hole in the protective layer of zona pellucida (see the image – the arrow) that surrounds the oocyte and then the embryo until the implantation (hatching in the uterus). AH helps the embryo to hatch from the shell which is a necessary condition for biopsy and thus the genetic examination of embryos in the blastocyst stage, and it is also necessary for embryo implantation into the uterus.
AH is performed on the 3rd day of the embryo culture, when the embryo is ideally made up of 7-10 cells. It is automatically done on the embryos of patients who require genetic testing of their embryos on day 5 or 6 of the culture by so-called PGT-M and PGT-A methods. 
The former terms PGD and PGS are replaced by new terms:
PGS = PGT-A (Preimplantation genetic testing for aneuploidies – abnormal number of chromosomes)
(Preimplantation genetic testing for monogenic/single gene diseases)
Furthermore, it is performed on embryos with significantly thick zona pellucida, which could prevent their hatching and subsequent implantation in the uterus.