Assisted Hatching is a procedure in which a hole is made in the egg shell just before embryo transfer. A protein coat, the zona pellucid, surrounds eggs and embryos. This functions to regulate fertilization by preventing more than one sperm from penetrating the egg, and also acts as protection during the early stages of development. However, to implant into the lining of the womb (the endometrium) and so establish a pregnancy, the embryo must first shed this coat, which it does usually on Day 6-7 of development by a natural process called hatching. At this point, the embryo is a hollow ball of cells called a blastocyst.
The most common point of failure of assisted conception treatments is after embryo transfer. It is believed that one cause of this is the inability of the transferred embryos to hatch, although why this is the case is as yet unclear. It has been suggested that current limitations of in vitro laboratory culture causes changes to occur to the zona, which make it more difficult for embryos to hatch. This does not affect the best quality embryos, but those of more borderline quality.
It is also thought that the cryopreservation (freezing) of embryos causes changes to the zona, which can reduce the incidence of hatching.
In order to counteract this, assisted hatching is now being offered at a number of centres and aims to improve the chances of successful hatching by the creation of a hole in the zona pellucid. There remain mixed views amongst the medical and scientific community as to whether the technique actually improves the chances of pregnancy, but most agree that it is not detrimental and may be potentially helpful in selected groups of patients.
There are several possible methods of carrying out assisted hatching. The most widely practiced being whereby a fine glass pipette is used to blow weak acidic medium on to the zona. This thins an area before a hole is punched through the centre of the thinned section. The procedure is carried out on day 3 of embryo development. By this time sufficient cell-cell bonding has occurred to minimize the loss of cells through the hole created.
A loser can also be used for making this hole and is now more commonly used.
Who is it appropriate for:
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Where there is elevated basal serum FSH (follicle stimulating hormone) in the woman (10 - 12 iu/l) |
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Where the female partner's age 40 years |
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Were falled implantation occurs after embryo thransfer of good quality embryos on two or more occasions |
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Where the embryos selected for transfer appear to have unusually thickened zonae |
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Where the cycle involves the transfer of frozen/thawed embryos. |
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