Assisted Hatching in IVF
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. Assisted hatching was developed in response to this theory that some women may fail multiple cycles of standard IVF because their eggs have a thicker shell. By creating a minor defect in the zona (shell) the result is a greater chance of the embryo "hatching," or shedding its shell, allowing for a better chance of implantation in the endometrium. 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. In our studies, assisted hatching had improved the success rate in women between 35 and 40 so much that it began exceeding the results of our women under 35.
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.
In our experience this relatively small variation in the IVF procedure has yielded dramatic results in older patients and those with previously failed cycles. 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 have a better prognosis with assisted hatching.
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.