Until shortly before implantation in the uterus, the egg, or the early embryo, is surrounded by a membrane, the socalled zona pellucida. The hatching of the embryo is the process during which the embryo leaves this egg membrane. This natural process, which is the result of individual processes and ends when the zona pellucida ruptures, is an important step towards the implantation of the released embryo. 

It is possible that under certain conditions the embryo cannot leave the egg membrane. This prevents implantation, and thus, pregnancy. The reason for this problem may be a particularly thick egg membrane, for instance, or a hardening of the egg membrane. Hardening of the egg membrane can be observed especially in the eggs of older women or in frozen eggs. However, there are indications that a hardening of the egg membrane may also already happen during the cultivation of the egg which is necessary in in vitro fertilisation. The latest and safest method for facilitating the hatching of the embryos (assisted hatching) is the application of a diode laser, which allows for a non-touch, precise reduction of the zona pellucida.