In this session, Sofia Rodrigues, Clinical Embryologist at Ferticentro, Coimbra, Portugal, has explained and discussed a new method called Non-invasive Preimplantation Genetic Testing (niPGT-A), its advantages and possibilities.
PGT-A – what is it?
Sofia started by describing what the PGT-A method is. She explained that
PGT-A means Pre-implantation Genetic Testing for aneuploidy, and it is performed on embryos to screen for numerical chromosomal abnormalities. An embryo is considered to be
aneuploid when it has extra or missing some chromosomes. These kinds of
embryos that are missing or have extra chromosomes often fail to implant, and they usually lead to miscarriage. On the other hand,
if implantation is successful, it can lead to a birth of a child with a genetic condition. The embryos that are found to be chromosomally normal are referred to as
euploids, and these
are the ones that are more likely to lead to a successful pregnancy and give a live birth of a healthy child.
We perform PGT-A to find euploid embryos, so typically,
we do the PGT-A before the embryo transfer so that we can have more information about the embryos before we transfer them. That way, patients can make informed decisions about the treatment and which embryos to transfer. It’s important to remember that PGT-A doesn’t make the embryos better, the embryos are what they are, we can just get more information with the PGT-A, and we have the advantage to gain the capacity to select the best embryo to transfer.
By knowing that that embryo is genetically normal, we can reduce the number of cycles needed to obtain a pregnancy. That way, we know that we are selecting a genetically normal embryo.
At Ferticentro, we perform
PGT-A with the use of Next Generation Sequencing (NGS). This is a specific genetic method that helps us learn the DNA of the embryos.
This technique allows us to analyse all the 24 chromosomes of each embryo.
PGT-A – how is it done?
To do the PGT-A on an embryo, we must do a biopsy. The biopsy consists of removing some cells directly from the embryo for them to be genetically analysed. To do the biopsy, we should have embryos at the blastocyst stage, and this stage is reached on day-5 or day-6 of culturing. Only the embryos that reach this stage and are of good quality are biopsied. To remove these cells, we use a laser system to open a little hole in the blastocyst, and then we just remove some cells. These pieces of cells are going to be sent to the genetic laboratory, and they will be doing the genetic analysis. At the clinic, we just do the biopsy itself and then cryopreserve the embryos and wait for the result of the biopsy.
PGT-A – is it useful?
There are a lot of studies on PGT-A that show us that PGT-A can be useful. One of the studies from Igenomix says that
women between the age of 38 and 40 years old undergoing IVF treatment have a 64% chance to have aneuploid embryos. Then
the rate of aneuploid embryos increases as the maternal age increases.
Another study from Igenomix shows a clinical outcome with and without PGT-A. Different rates are presented, such as implantation rates, delivery rates per transfer and miscarriages rates.
The implantation rates increase significantly when we do the PGT-A. In the delivery rates per transfer, there is a higher rate of deliveries when we do the PGT-A, also
there is a decrease in the rate of miscarriages when we do the PGT-A because we know that we’re transferring only good and genetically normal embryos. Therefore, it shows that it makes sense to do the PGT-A to achieve pregnancy in a shorter time.
Non-invasive PGT-A (niPGT-A)
Non-invasive PGT-A is a new technique that is still being studied. Thanks to this method,
we can actually know the genetics of each embryo without touching the actual embryo, without damaging it. The biopsy of the embryo itself is a pretty invasive procedure, and it’s risky for the embryo because it may not resist the biopsy, and we can lose the embryo. This new technique has a lot of advantages compared to the traditional PGT-A. How is it done?
The embryos are in a culture medium where they are going to grow until they reach the blastocyst stage. During that time,
the embryo naturally releases DNA during their development, and we can collect that culture medium and send it to the genetic laboratory, where they will search for DNA and the genetics of the embryos to see if they are genetically normal or abnormal.
This gives the same result as the traditional PGT-A, but we don’t need to touch the embryo, which is a big advantage of this new technique.
niPGT-A – is it effective?
Some studies from Igenomix show that this technique can be quite effective.
Igenomix did a study where they
studied 1300 human blastocysts, and they
compared the DNA that was released by the embryo to the culture media and from the biopsy of the blastocyst. They compared these two DNAs from the same embryos, and they found that there was,
on average, 78.2% of concordance between these two DNAs. The concordance between the DNA in the medium and the DNA from the biopsy of the two trophectoderm cells was 87.5%. The concordance between the DNA of the medium and the biopsy of the inner cell mass was 84.4% which is a really good result. 80% of concordance between these two types of DNA shows that this technique can give us a big advantage in the future.
We can conclude that this
non-invasive approach can avoid the actual embryo biopsy while giving us the genetic result of the embryo. Although it is still an experimental technique, some clinics already use this as a diagnostic technique. We don’t use this technique at Ferticentro yet, but we are in the validation phase. We are now sending samples to Igenomix to see if our samples are concordant enough so we can use this in the future. It looks very promising, and we will be able to use this technique in the future for all the patients.
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