Why Perform Assisted Hatching?
There is another critically important component of the embryo that is often overlooked, the zona pellucida (ZP) or the egg shell. The zona pellucida is secreted by the egg and has several important functions, such as:
i) During fertilization, it serves to prevent the access of more than one sperm to the egg.
ii) it keeps the cells of the embryo together during early development, until the embryo reaches the blastocyst stage. At the blastocyst stage, the embryo has enough structural integrity that it no longer needs the protection of the ZP and the embryo “hatches”. A higher implantation rate is observed in patients undergoing IVF, who had the ZP of their embryos mechanically opened.
Who Needs Assisted Hatching ?
The following patient groups may benefit from assisted hatching : women older than 36 years of age, those with elevated FSH levels, couples with previous IVF failures, embryos with an abnormal appearing zona pellucida, and when using cryopreserved embryos.
How is Assisted Hatching Performed?
There are a number of ways to introduce a hole or a weakness into the zona.
Mechanical: Some embryologists will perform assisted hatching by mechanically piercing the ZP with a specifically designed pipette.
Chemical Erosion: involves exposure of the embryo to an acidified media called acidified tyrodes solution. This acidic solution is microscopically applied to the ZP to induce thinning.
Laser: This specifically designed laser system includes the laser, which serves as the energy source to create an opening in the ZP, and a computer which allows the operator to precisely control the laser energy output, laser pulse duration, and gap size. This system has many benefits when compared to the more standard mechanical and acidified tyrode’s techniques.
The computer assisted laser method is more precise, resulting in a more consistent ZP opening. Laser assisted hatching takes less time and does not expose the embryos to potentially adverse chemicals, so embryos spend less time out of the optimal culture conditions of the incubator.
The cumulative effect of these factors is to minimize the stress placed upon the embryo during the performance of assisted hatching. This in turn translates into improved implantation and pregnancy rates.