This technique is applied on embryos prios to their transfer in the uterus and it involves thinning of the zona pellucida that surrounds the embryo throughout the preimplantation period. The role of the zona pellucida is to protect the embryo, by aiding in keeping its integrity inside the reproductive tissue and from pathogens or microorganisms that may attack the embryo before implantation.
Under natural conditions, the environment of the uterus, at around the 6th day of development, the zona pellucida is disrupted in order for the embryo to come in contact with the endometrium and initiate implantation. Sometimes, the zona is not disrupted properly and acts as a “trap” for the implantation of the embryo. This happens when the zona is hardened, it prevents its removal from around the embryo and therefore the embryo fails to implant. An increased risk of hardening of the zona has been observed in women of advanced maternal age.
During assisted hatching the zona pellucida is thinned with the aid of a laser, which punctures a whole, which will aid the natural process of the embryo. It is performed a few hours before embryo transfer, and only in those embryos that it is necessary. With assisted hatching, embryos with a thicker than normal zona will have an increased chance of successful implantation.