Assisted zona hatching (AZH) is a procedure of assisted reproductive technology,mainly used in IVF, in which a small hole is made in the zona pellucida. It can be done using different methods including mechanical, chemical or by the use of lasers, thereby facilitating zona hatching.[1] Zona hatching is where the blastocyst gets rid of the surrounding zona pellucida to be able to implant in the uterus.
A systematic review and meta-analysis came to the result that assisted zona hatching is related to increased rates of clinical pregnancy and multiple pregnancy in women with previous repeated failure or frozen-thawed embryos.[2] However, it is unlikely to increase clinical pregnancy rates when performed in fresh embryos transferred to unselected women, to those without poor prognosis or to women of advanced maternal age.[2] Also, overall, there no evidence of a significant difference in live birth rate following assisted hatching compared with no assisted hatching.[3]
Assisted Hatching it is not always recommended, it is mostly applied in case of:
-Implantation failure
-Advanced age
-Anomalous zona pellucida (thick, partitioned,...)
-Thawed embryos
-Blastocyst biopsy
Mechanical assisted hatching: involves the use of micromanipulation techniques by using a needle. It's not very often used because it has a higher risk of damaging the embryo. It is also called "partial zona dissection".
Chemical assisted hatching: involves the use of specialized solutions (mostly acid, e.g. thyroid acid) in order to degrade the zona pellucida. Because it can be toxic for the embryo, it needs to be washed.
"Laser assisted hatching" (LHA): a high energy laser is used to create an opening in the zona pellucida, it is the most precise technique and safe for the embryo but it is the most expensive one.