Assisted hatching: An interview with Cristina González, Ovoclinic laboratory director

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Assisted hatching is a complementary technique carried out in the IVF laboratory.

The 5 day old embryo, called the blastocyst, is surrounded by a “shell”: the zona pellucida. The zona pellucida is the protective layer that surrounds the egg cell and is maintained throughout embryo development until the embryo is able to hatch from it, which should occur naturally, before the embryo can implant in the endometrium.

The assisted hatching technique involves making a small hole in the zona pellucida to help the blastocyst break out of it. This allows the cells of the trophectoderm, cells that are directly involved in implantation, to be exposed to the uterine environment, meaning that communication occurs between the embryo and the uterus, on a molecular level.

This procedure is non-invasive and does not jeopardize the embryo, therefore, it can be applied to all those embryos that haven´t hatched by themselves, as hatching is indispensable for the implantation process.

Since it is a technique which often generates doubts and questions amongst patients, Cristina González, embryologist and Ovoclinic Laboratory Director, has invited us into her laboratory so she can answer the following frequently asked questions:

DOES ASSISTED HATCHING PROMOTE EMBRYO IMPLANTATION?

One of the advantages of assisted hatching is that it promotes implantation in those cases where the embryo has not been able to hatch by itself naturally. As we have commented previously, the process of hatching refers to the moment when the blastocyst makes the zona pellucida (ZP) thinner, by a process of expansion and contraction, until the ZP breaks and the blastocyst can leave and find its way to the endometrium to implant itself. At Ovoclinic, if we observe that the embryo has not hatched naturally, we will carry it out in vitro in our laboratories using a laser, which is the quickest and simplest way.

WHEN IS HATCHING PERFORMED?

Assisted hatching can be carried out on different days of embryo development, depending on the protocols of each laboratory. Specifically, at Ovoclinic, we perform assisted hatching on day five (D+5) because it is the day on which we remove the embryos from the incubator to evaluate them and decide which one we will transfer.

The idea is to disturb the embryos as little as possible, which you achieve by not taking them out of the incubator unless it is absolutely necessary. We always cultivate the embryos to the blastocyst stage because of the advantages and increased pregnancy rates of doing so. Therefore, it is in the same moment, on day five, we do the assisted hatching.

ONE OF THE ADVANTAGES OF ASSISTED HATCHING IS THAT IT FACILITATES IMPLANTATION IN THOSE CASES WHERE THE EMBRYO HAS NOT BEEN ABLE TO HATCH NATURALLY.
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HOW LONG DOES IT TAKE AND IS IT EFFECTIVE FOR ALL EMBRYOS?

It’s a very quick procedure. Assisted hatching is performed in a matter of seconds, and as such the embryos do not need to be out of the incubator for too long. It is effective for all favorably developing embryos, and helps the embryo to shed its outer later without effort so it can implant into the endometrium.

Furthermore, this technique is recommended for all embryos presenting with hatching difficulty, previously frozen embryos which have a hardened zona pellucida or patients who have suffered with previous, recurrent, implantation failures.

CAN IT BE PERFORMED ON FRESH EMBRYOS TO BE TRANSFERRED AND ON FROZEN EMBRYOS?

It can be done in both cases, and each laboratory has its own preference. We perform assisted hatching on all viable and correctly developing embryos on day five, and so apply this technique to blastocysts transferred fresh, as well as those that have been cryopreserved.

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