embryo transfer Laboratory

Assisted hatching to aid embryo implantation – What is it? And when is it recommended?

assisted hatching

One of the most important steps in fertility treatment is the implantation of the embryo. However, if implantation is not successful even after examining the embryo and ruling out all possible factors, Assisted Hatching is recommended. With this technique, the presence of a thickened outer membrane (also called zona pellucida) which prevents the embryo from exiting and thus implanting in the endometrium can be determined.

But what is the zona pellucida?

The zona pellucida is the name given to the outer layer of the embryo from which the embryo detaches between days 5 and 7 of development in order to implant in the endometrium.

Among other things, this membrane has the task of preventing multiple sperm from entering the egg, controlling the first cell divisions of the embryo (by ensuring that these cells do not disintegrate until day 4), and preventing premature implantation of the embryo.

“Hatching” – This is what happens when an embryo hatches

The natural process of the embryo on day 5 or 6 of its development (blastocyst) to detach itself from the zona pellucida in order to implant in the uterus is called hatching.

How does the embryo manage to free itself from the zona pellucida on day 5? The so-called blastocyst cavity forms, fills with fluid, grows and stretches until the pressure exerted by the embryo on the membrane tears the zona pellucida. This allows the embryo to emerge and implant in the uterus.

However, some women, especially those over the age of 35, may have a very hardened layer that prevents the embryo from hatching on its own after fertilisation of the egg, thus preventing pregnancy.

Blastocysts: Development and Hatching

Depending on the day of development, the condition of the zona pellucida and the appearance of the embryo, we distinguish between 3 types of blastocysts:

  • Expanded blastocyst: The embryo is large and the zona pellucida is thinner.
  • Hatching Blastocyst: The zona pellucida has ruptured and the embryo is hatching.
  • Hatched Blastocyst: The embryo has already completely detached from the zona pellucida.

Assisted hatching

Why do we perform Assisted Hatching?

The laboratory technique known as Assisted Hatching consists of perforating the zona pellucida of the embryo with a tiny hole prior to embryo transfer to facilitate implantation. This technique is performed additionally to in vitro fertilisation, as well as used as part of the ICSI technique to inject the sperm into the egg.

In addition, this procedure is often used to perform preimplantation genetic diagnosis (PGD/PGS) techniques , which involves making an incision in the zona pellucida to remove a cell to analyse its genetic make-up.

Assisted Hatching: When and how is it performed?

Generally, Assisted Hatching is performed on the 3rd day after fertilisation, when the embryo has about 8 cells and has not yet increased in size.

There are 3 possible techniques for this procedure:

  • Chemical hatching: Tiny amounts of acid are applied to the zona pellucida until the shell is breached.
  • Mechanical hatching: A needle is passed through the zona pellucida which is then punctured by friction with the pipette. Due to the risk of damaging the embryo, this technique is rarely used.
  • Laser-assisted hatching: This is the method used in all clinics belonging to the IVF-Life Group, as it provides better control and safety when perforating the zona pellucida, as only a few micropulses of a laser are needed.

Assisted hatching

Assisted Hatching is a complex technique. To avoid damaging the embryo in all three methods, an inverted microscope must be available, equipped with an attached micromanipulation system to perform the procedure with precision and caution

When and for whom should Assisted Hatching be performed?

The most common situations in which this technique is used are:

  • Embryos with slow and fragmented development or division.
  • Embryos with a thick, dark zona pellucida or with other alterations.
  • Previous implantation failures.
  • Patients over 37 years of age.
  • In cases of transfers with cryopreserved embryos, due to the fact that in many cases the zona pellucida tends to harden.

Assisted Hatching is not a routine procedure. It is not performed on all patients but only recommended in certain cases. At IVF-Spain Madrid, we look closely at each patient’s circumstances and provide an individual and detailed diagnosis. This allows us to recommend Assisted Hatching to our patients in cases where the embryo needs help with implantation.

Assisted Hatching and its importance for your fertility treatment

Thanks to Assisted Hatching, in cases of repeated implantation failures or when working with cryopreserved embryos, we can overcome one of the biggest challenges and help our patients when hatching does not occur naturally.

As experts in the field of assisted reproduction, we know that embryo hatching is an important and decisive stage for implantation and subsequent successful pregnancy.

For this reason, we at IVF-Spain Madrid are committed to innovative technologies and treatments, and also specialise in complex cases. In our clinics, we carry out detailed examinations with the aim of better understanding your reproductive health and determining which technique is best for you, thus increasing implantation and pregnancy rates.

If the theory still doesn’t convince you and you have any further questions, do not hesitate to request an initial online consultation appointment with one of our fertility experts.

We offer the guidance and professionalism you need to start your own family.

About the author


At ProcreaTec, we understand the road toward a healthy pregnancy is not always easy. Through this blog, we want to reach out to all who are struggling on the path of infertility to find support. If you have any questions or would like to tell us about your situation, you can comment on the posts or send us an e-mail.
If you would like to learn more about our clinic, we invite you to visit our website en.procreatec.com
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