A protective membrane is present around the embryo after the oocyte and the fertilization stages. This membrane is called zona pellucida.

The most important functions of this membrane in the structure of glycoprotein are as follows:

1. Takes role in the fertilization of the egg and the nutrition and development of the embryo. Takes role in the unification of the egg and the sperm.

2. Prevents polyspermia; when an egg is fertilized by a sperm, this membrane prevents other sperms from entering into the egg.

3. Protects the embryo and provides its integrity.

Today, in test tube baby centres, embriyo is transferred into the womb of a woman on the 3rd day following the collection of the eggs. At that moment the embryos are 6-8 celled.

When embryos reach to the blastocyst stage, the surrounding membrane cracks or perforates spontaneously. This is called hatching. With the perforation of the membrane, the blastocyst gets out of the membrane and directly contacts the endometrium tissue and attaches. In some cases it is considered that this event is getting difficult or does not occur at all.

In test tube baby applications, the process of thinning the outer membrane around the embryo with acides, mecahanical or with the help of laser before conducting embryo transfer is called Assisted Hatching. A hole that will be opened in ZP facilitates natural hatching. The purpose in conducting this process is to increase the chance of the embryo to attach itself (implantation).

Assisted hatching process is conducted with different techniques:

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Laser beam passes through the objective of the microscope, releases its energy to ZP macromolecules and the liquid in the ZP at the focal point. Thermal effect occurs; melting is formed in ZP due to increase in the temperature. The hole is regular, limited and controlled.

To whom assisted hatching is applied?

1. Repeated IVF failure

2. Woman’s age > 35

3. Frozen embryo transfer

4. Thick ZP (>15 µm): ZP thickness and rigidness

5. Abnormal ZP/ preembryo shape: ZP is totally or partially double-deck in oval shaped oocyte and embryos.

6. Thick cytoplasm

7. Cytoplasmic fragmentation