One of the most frustrating aspects of assisted reproductive technology for patients and fertility professionals alike is dealing with failure. This is especially true in couples who have attempted assisted reproductive procedures many times, and also in those whose time is running out because of their age. Assisted hatching offers hope to couples who fall into these categories.
Assisted hatching was developed from the observation that embryos which had a thin zona pellucida (shell) had a higher rate of implantation during in vitro fertilization. It was postulated that creating a minor defect in the zona might result in a greater chance of the embryo "hatching," or shedding its shell, allowing for a better chance of implantation in the endometrium.
Initial controlled trials at New York-Cornell Medical College showed a marked increase in implantation in women over age 35 and particularly over 38 or with an elevated FSH level on day 3 of the menstrual cycle. Couples with multiple failed IVF cycles also appear to benefit from assisted hatching. Assisted hatching may be helpful in these infertile couples because their embryos lack sufficient energy to complete the "hatching" process. It is thought that some women may fail multiple cycles of IVF because their eggs have a thicker shell therefore they have a better prognosis with assisted hatching.
In addition, hatched embryos implant one day early, which may allow a greater opportunity for implantation to occur, particularly if the endometrium is advanced by the ovarian stimulation.
The addition of assisted hatching to the standard IVF protocol does add extra laboratory manipulation. There is a small risk of damage to the embryo during the micromanipulation process or at the time of transfer, and there may be a slight increase in identical twinning compared with regular IVF. We have not observed a higher rate of identical twins than with routine IVF. This may relate to whether a large enough opening is made in the zona to prevent pinching of the embryo during the hatching process.
The IVF cycle is conducted in the routine manner until the evening of the day of retrieval, when the patient is started on four days of a steroid and an antibiotic to protect the embryo from inflammatory cells. The fertilized embryos are allowed to develop until the third day following the retrieval, since the more advanced embryo is more resistant to the effects of inflammatory cells.
The assisted hatching procedure, like ICSI, is carried out by a technique known as micromanipulation. In small dishes the embryos, which now contain an average of six to eight cells, are stabilized by a holding pipette, while on the opposite side a small pipette containing acidified Tyrode's solution creates a small defect in the zona. The size of the defect is critical; if it is too small it may pinch off the embryo during hatching and either reduce the chance of implantation or cause identical twinning. The embryos are then rinsed to remove any excess acid solution and returned to the incubator for a few hours before transfer into the uterus.
In our experience this relatively small variation in the IVF procedure has yielded dramatic results in older patients and those with previously failed cycles.
The assisted hatching procedure, like ICSI, is carried out by a technique known as micromanipulation. In a small dish this eight cell embryo is stabilized by a holding pipette on the left, while on the opposite side a small pipette containing acidified Tyrode's solution creates a small defect in the zona.