A covering layer, or shell, that surrounds the embryo is called the zona pellucida. The zona has an important role in fertilization as it allows only one sperm to penetrate the zona and enter the egg to achieve fertilization. It also acts to prevent premature implantation in the Fallopian tube and may help prevent the early embryo from being attacked by cells of the immune system.
The embryos have to hatch or break out of the zona in order to embed into the endometrium lining within the uterine cavity. This occurs about four to five days after embryo transfer when the embryo is at the blastocyst stage. Naturally this takes place by expanding/contracting of the zona until it breaks, allowing the blastocyst to hatch.
If the zona is not functional, this hatching may not occur. It has been reported that up to 75% of normal embryos never hatch through the protective layering. Laboratory techniques involved in IVF may result in hardening of the zona. In natural fertilization there are enzymes present within the fluid in the Fallopian tube, which may “soften” the zona. This may not happen in IVF as the tube is bypassed. The zona may also be thicker following IVF, especially in older women. Frozen embryos may also have a hardened zona.
Laser Assisted Hatching
At the Center for Advanced Reproductive Medicine & Fertility, we use the latest laser technology to perform assisted hatching. Laser hatching is fast, safe, simple and highly repeatable unlike the old method of hatching that used acidic medium expelled onto the zona to create a small hole.
The zona is drilled by the microlaser system creating a clean-cut precise incision in the zona.
This is more accurate for several reasons :
- The process is fast compared to the older chemical and manual methods, thus the embryo does not have to be held still by a suction pipette. As well as this factor, we use a vibration-free table to avoid any accidental movement of the embryo.
- The accuracy of the laser is predetermined by its programming, and is therefore greatly reduces the possibility of operator error. There is a high degree of accuracy.
Who could benefit from assisted hatching?
At the Center for Advanced Reproductive Medicine & Fertility patients who will be considered for laser assisted hatching are:
- Patients undergoing IVF/ICSI for the first time, who are considered poor responders because they have required a high dose of gonadotropins for poor ovarian response.
- Women who, regardless of age, have had two or more embryo transfers but no implantation.
- Patients whose embryos have a zona pellucida that appears to be thicker than average, as determined by an embryologist during an IVF or ICSI cycle.
- Women who are undergoing FET (frozen embryo transfer cycles).
The likelihood of improved chances for pregnancy is assessed medically before recommending laser assisted hatching.