Assisted Hatching (AH) is a micromanipulation procedure that increases chances of pregnancy. It is performed prior to embryo transfer. An embryo needs to escape from its protein shell, called the Zona Pellucida (a protective layer), before it can implant in the uterus. The assisted hatching procedure involves thinning or making a small hole in the Zona Pellucida just before the embryos are replaced, whether they are fresh or frozen/thawed. The process is repeated for each embryo.
Research has shown that assisted hatching is beneficial for certain groups of patients only. However, when the patients are selected on definite criteria, it can produce a significant improvement in success rates. There are several indications for assisted hatching:
- Female over 38 and using their own eggs. As a woman ages, her eggs also undergo changes by thickening of the protective layer. For this reason, assisted hatching is particularly useful for older women
- Previously unsuccessful IVF cycles
- Women whose embryos exhibit thick Zona Pellucida
- Women with elevated day 3 Follicle Stimulation hormone (FSH) levels
- Couples having IVF with poor quality embryos
There is no clear benefit of AH to improve pregnancy or live birth rates in other groups of IVF patients.
The most common techniques for AH used today are:
• Mechanical hatching
• Acid Tyrode hatching
• Laser hatching
• Pronase thinning
Before being transferred to the uterus, a hole is made in the outer layer of the embryo or it is thinned, using acid, laser or mechanical methods. It is important that the size of the hole created in the zona is large enough to avoid trapping the embryo during hatching, but not large enough to permit blastomere loss.
On day three of embryo development, the embryologist uses either weak acid in a fine glass pipette, a microlaser or a microtool to thin or cut a hole in the Zona Pellucda of the embryo. The embryo is held with a specialized pipette. The embryo is then washed and put back in culture in the incubator. Because assisted hatching thins or makes a hole in the protective outer layer around the embryo, the woman may be given antibiotics to prevent infection.
The embryo transfer procedure is done shortly after the hatching procedure. Embryo transfer places the embryos in the woman's uterus where they will implant and ideally develop resulting in a live birth.
A lot of couples who are undergoing the IVF process decide to try assisted hatching. The success rate of assisted hatching varies widely between different clinics. This could be due to differences in their patient populations, the overall quality of the lab, skill of the individual performing the hatching, the hatching technique used and other factors. The benefit of assisted hatching is not seen in all IVF programs, but it can result in greater likelihood of implantation.
The risk of damage is very small (1%) when an experienced embryologist performs the procedure. Current research suggests that this treatment is no more likely to cause an abnormality to the baby than IVF without assisted hatching. AH has been implicated in an increased rate of monozygotic twins. The cause of this is that the technique used to thin out the protective layer can also sometimes split the embryo into two halves.