Assisted Hatching (AH) is a relatively new micromanipulation technique that can increase your chance of in vitro fertilization (IVF) treatment success. Usually, an embryo needs to escape from its protein shell, called the Zona Pellucida (a protective layer), before it can implant in the uterus. Sometimes embryos have a hard time hatching out of this protective layer. This can occur if the Zona Pellucida is too thick or if the embryo does not have enough energy to break through the layer. It is observed that embryos which have a thin Zona Pellucida have a higher rate of implantation during in vitro fertilization.
Based on this observation, the assisted hatching procedure was developed. It involves thinning or making a small hole in Zona Pellucida just before the embryos are replaced, whether they are fresh or frozen. The process is repeated for each embryo.
Assisted hatching is particularly recommended for couples who are most at risk of poor IVF outcomes.
The most common indications for assisted hatching are:
- Age factor: female over 38 and using own eggs
- Women with elevated Follicle Stimulation Hormone (FSH) on day 3 of their menstrual cycle
- Previous failures of IVF cycles
- Women whose embryos display thick Zona Pellucida
- Embryo quality – couples having IVF with poor quality embryos
When using cryopreserved embryos
Assisted hatching (AH) is a very delicate procedure and is done while the embryo is in the laboratory. It is performed under a microscope, during the embryo development. During the assisted hatching laboratory procedure, the embryo is temporarily held in place with a narrow pipette and a tiny hole is made, depending on the method. It is essential that the size of the hole created in the Zona Pellucida is large enough to avoid trapping of the embryo during hatching, but not large enough to allow blastomere loss.
A chemical, mechanical or laser methods can be used to dissolve part of the Zona Pellucida to smooth the progress of the hatching process later. The assisted hatched embryos are then transferred into the uterine cavity. The embryo transfer procedure is done shortly after the hatching procedure. Embryo transfer places the embryos in the woman’s uterus where they will hopefully implant and develop.
The most common techniques used nowadays are:
Mechanical hatching – In this case, assisted hatching is done by mechanically piercing the Zona Pellucida with a specifically designed pipette. A solid needle with a microscopically fine point is applied to mechanically drill and remove a limited amount of material from the embryo’s zona pellucida, leaving behind a small hole on its surface.
Chemical hatching – The embryo is exposed to an acidified solution. An extremely fine needle is used to apply a small dose of the agent to the embryo’s zona pellucida. A hole appears due to the acidic reaction and then the embryo is washed of the acidic solution.
Laser hatching – Laser-assisted hatching is a very common procedure. It involves laser, which serves as the energy source to create an opening in the Zona Pellucida. The laser energy output, laser pulse duration, and gap size is carefully controlled by the operator with the help of computer.
Assisted hatching is associated with high success rate and it offers improvements over standard IVF treatments. Some advantages of assisted hatching are that this procedure requires less number of embryos for transfer and these embryos have a better chance of developing to their blastocyst stage before implantation.
Although, the success rate of assisted hatching varies widely among fertility clinics. This could be due to variation in their patient populations, the general quality of the laboratory, experience 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.
Unfortunately, it is possible to damage embryos with assisted hatching but the risk of damage is very small (1%) when an experienced embryologist performs the procedure. Assisted hatching can cause an increased rate of monozygotic twins. This is due to the micromanipulation technique used to break through the Zona Pellucida that can sometimes cause the embryo to split into two identical halves. Assisted hatching can also be associated with an increased risk of infection.