What is hatching in human?
Unlike in birds and in some reptiles, where Hatching means coming out of a biologically complete replica of that animal, by breaking an outer shell, in humans it indicates just a beginning of a long journey. After the union of a male and a female gamete in the fallopian tube-, which is also called as fertilization- an embryo, is formed which travels to the uterus. By the time it comes to the uterus, it reaches a stage called blastocyst. The core portion of this blastocyst- the Inner Cell Mass (ICM)-has to implant into the endometrium, the inner lining of the uterus, to begin the formation of a baby. The process of coming out of this ICM through a small opening of the soft, porous, protective layer called Zona Pellucida of the blastocyst, is called as hatching.
Why it is necessary to assist this natural hatching process?
Usually, an embryo prepares itself for hatching by thinning out the zona through its growth stages. Under some circumstances, the zona remains thick and rigid which prevents ICM to come out on its own, thus hindering the process of implantation. During In Vitro culture, this zona thickening is observed more often in -older patients (Age > 40 years), during prolonged culture, due to impaired culture conditions, in patients with indications like severe endometriosis, in patients with elevated basal FSH levels, after using hyaluronidase for removal of cumulus and corona during ICSI and sometimes after cryopreservation. In these cases, assisted hatching is suggested to enhance implantation and thus improve clinical pregnancy rate.
How assisted hatching is done?
Assisted hatching can be done by three methods -1. Mechanical hatching. Here, part of the zona is sliced off using finely drawn micropipettes while holding the embryo with another specially made micropipette.. -2. Enzymatic hatching. Here, part of the zona is dissolved using a diluted and otherwise safe proteolytic enzyme like acid tyrode.
And -3. Laser assisted hatching. Where, part of the zona is drilled in one plane using a safe intensity laser beam.