This procedure consists in incising the embryo’s zona pellucida (making small slot in the zona) before it is transferred to the uterine cavity. Cells which form an early embryo are surrounded by a membrane called zona pellucida. During a normal development, this zona partially dissolves and the embryo cells can get outside it. Only this release of the embryo from the zona allows its implantation in the uterus, enabling the direct contact between the embryo and endometrium.

In normal circumstances, the blastocyst expands and presses the zona from inside, until at some point in time the zona breaks. Further expansion of the blastocyst makes it easy for it to leave the zona completely.

This phenomenon is called a blastocyst hatching.

In many cases under in vitro and in vivo conditions, zona pellucida does not break naturally. The embryo is somewhat imprisoned and does not have the possibility to implant. AH may be carried out on the day of embryo transfer, just before the ET procedure, by an embryologist using laser technique or mechanical or chemical methods.

The AH procedure is most often carried out on day 5 of embryo development when the space between the embryo and the inner wall of the zona is still quite large (this has a great impact on the performance).

In cases where AH is carried out in thawed embryos, it is possible to conduct this procedure also in thawed blastocysts (which are usually frozen on day 5 of their development) when they are still shrank and the risk of injury to the embryo is low.

The successful and safe outcome of the procedure depends also on the expertise of the embryologist who can determine properly the site and manner of incising the zona.

The AH technique may increase the chances for implantation of any embryo, especially in case of the above-average thickness of zona pellucida confirmed in the laboratory, in female patients aged 37 years or older, in case of thawed embryo transfer (the patient’s age as well as embryo freezing and thawing is related to zona hardening) or in couples who have failed to get pregnant following previous IVF cycles (2 or more failed IVF cycles, cycles with poor embryo quality).

The risk associated with performing the AH is low, but the risk of embryo damage which may lead to the total loss of the embryo cannot be totally excluded. Some claim that AH can also increase the chances of obtaining a multiple monozygotic pregnancy with a typically somewhat more complex course.

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Published: 3 November 2015 Updated: 3 April 2017