Implantation of the embryo is one of the most important steps in an assisted reproductive treatment. In many cases in which the embryo has been examined and all possible factors have been ruled out, but implantation has not been successful, it is recommended to use the Assisted Hatching technique to rule out the presence of a thickened outer membrane (also called zona pellucida), which prevents the embryo from exiting and thus implanting in the endometrium.
Let’s start from the beginning: What is the zona pellucida?
The outer layer of the embryo is called the zona pellucida. The embryo detaches from this layer between days 5 and 7 of development to implant in the endometrium.
Among its protective functions, this membrane prevents the entrance of multiple spermatozoa into the egg, it controls the first cell divisions of the embryo, as the zona pellucida ensures that these cells remain together until day 4 and do not disintegrate, and it prevents the embryo from implanting prematurely.
What is embryo hatching?
Hatching is a natural process where the blastocyst (embryo on the 5th or 6th day of development) manages to detach itself from the zona pellucida and thus achieve implantation, which will lead to pregnancy.
But how does the embryo break through this protective layer on day 5? The embryo has to use pressure so that it can tear the zona pellucida. This is why it forms what is called the blastocyst cavity, giving rise to the name blastocyst. This cavity fills with fluid, grows, expands and exerts pressure on the zona pellucida until it ruptures, helping the blastocyst to break free and implant in the uterus.
However, for some women, especially if they are over the age of 35, this layer can be very hard, preventing the embryo from hatching on its own once the egg is fertilised, and therefore preventing pregnancy.
Blastocyst development and hatching
Depending on the day of development, the state of the zona pellucida and the appearance of the embryo, the blastocyst can be classified into 3 types
- 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.
What is the purpose of Assisted Hatching?
Assisted Hatching is a laboratory technique that complements in vitro fertilisation . It consists of perforating or making a small hole in the zona pellucida of the embryo, prior to embryo transfer, in order to facilitate implantation.
We also perform this procedure during the ICSI technique in order to inject the sperm into the oocyte. It is also often used to perform preimplantation genetic diagnosis (PGD) techniques, as we need to perforate the zona pellucida in order to extract a cell and examine its genetic makeup.
When and how is Assisted Hatching carried out?
In general, Assisted Hatching is performed on day 3 after fertilisation, when the embryo usually has about 8 cells and has not yet increased in size.
Regarding the methods, there are 3 possible techniques:
- 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.
As this is a complex technique, in order to avoid damaging the embryo in all three procedures, it is necessary to be equipped with an inverted microscope connected to a micromanipulation system so that the procedure can be carried out with utmost precision and caution.
Who are ideal candidates for assisted hatching?
The most common situations in which this technique is used are:
- Patients over 37 years of age.
- Embryos with a thick, dark zona pellucida or with other alterations.
- Embryos with slow and fragmented development or division.
- Previous implantation failures.
- In cases of transfers with cryopreserved embryos, due to the fact that in many cases the zona pellucida tends to harden.
However, Assisted Hatching is not routinely performed on all patients. It is only recommended in specific cases. Therefore, at IVF-Spain we study the individual factors of each patient and carry out a precise and detailed diagnosis so that we can recommend this procedure when the embryo needs assistance in order to implant.
The importance of this technique in your assisted reproduction treatment
As experts in assisted reproduction, we know that the moment of embryo hatching is crucial and a decisive moment for implantation and the future of a successful pregnancy. Thanks to Assisted Hatching, we can overcome one of the most difficult obstacles in cases of repeated implantation failures or when we work with cryopreserved embryos: the failure of the embryo to hatch naturally.
At IVF-Spain we offer innovative technology and treatments and specialise in complex cases. We carry out detailed assessments with the aim of better understanding your reproductive health and determining which technique is best for you, increasing implantation and pregnancy rates.
If the theory does not yet convince you and you have further questions, do not hesitate to request an appointment for an initial online consultation with our team of fertility experts. We offer the guidance and professionalism you need to start your own family.