In this live event, Dr Christos Roukoudis, Gynaecologist & Fertility Specialist at IVF-Life Alicante, Spain, has talked about PGT-A and answered a question whether there are any benefits of doing PGT-A for embryos from donor eggs and explained how PGT-A works and when it is recommended.
Dr Christos Roukoudis, first explained that PGT-A (Pre-implantation Genetic Testing for aneuploidies) is a test for chromosome copy numbers that can be used during IVF to help determine the chromosomal status of an embryo from a biopsy of one or more cells. The results can help select an embryo with a normal number of chromosomes, the so-called euploid. But also, it can help us to avoid the ones that have an abnormal number of chromosomes, called aneuploid embryos. They may result in a higher tendency of an IVF failure or a miscarriage.
The number of oocytes starts to decrease after the woman is birth, as shown on the graph. Starting with puberty certain cohort of the oocytes are always recruited, and only one wins the race and becomes dominant. With increasing age, not only does the amount of eggs decreases but also egg quality is decreasing. Those oocytes accompany women during their reproductive life and also are vulnerable to damage in the DNA that they possess. This is one of the reasons why it’s so difficult to have success with own eggs in advanced reproductive age.
Every cell we have has 22 chromosome pairs and depending on the gender, we have an additional XX copy, or if it’s a male, it’s an XY. For a healthy child to be born with a normal number of chromosomes, the eggs available for fertilization must undergo a process of producing or having only one copy of each chromosome. This process is called meiosis, a similar process that occurs in the sperm of the male. The result is that the new life that is created possess 50% of the chromosome of each partner.
With advanced reproductive age, this meiosis process is disturbed and oocytes created have additional copies or don’t have any. This lack of integrity in the oocytes can result in unhealthy embryos that will not implant or lead to an early miscarriage, normally before the 12th week. It can also result in a child with a genetic disease, which happens less often. As shown on the graph, the risk is significantly increased with advancing maternal age, we see that Down syndrome, Edward’s syndrome is more likely to happen compared to a younger age.
PGT-A was suggested as a tool to identify those unhealthy embryos. Trisomy 21, Down syndrome and PGT-A testing have become routine methods for IVF to determine whether human embryos are to be clinically utilized or disposed of. The idea is that before an embryo transfer, we want to rule out the aneuploid embryos and only work with the healthy ones to increase the success rates.
Between the late 90s and now, some important events occurred, such as a single polar biopsy, biopsy of the first and the second polar body, the biopsy done on day-3, the cleavage stage, and then at the blastocyst stage when we perform PGT-A.
First, we have to perform the stimulation to obtain as many oocytes as possible. When the follicles reach a certain size, we do the egg retrieval, once we have the oocytes in the laboratory, the fertilization follows, the embryos will start to develop and on day-5, we’re going to perform PGT-A analysis, and we’re going to freeze them right away because we need to wait for the results almost 3 weeks.
How is the PGT-A test performed? Our biologists take around 6-7 cells from the cells, which are going to form the future placenta called trophectoderm, and we analyse it in our lab. When we finally have the analysis performed by Next Generation Sequencing (NGS), we can see if and in which chromosome pair we have an extra chromosome or possibly a missing chromosome, for example, it’s chromosome 13. As seen on the slide, there is PGT-A analysis done on several embryos, after an IVF cycle, a good amount of embryos was obtained, you can see that many embryos are abnormal, so they’re not suited for a transfer and out of those 5 embryos only 1 is normal.
In the proposed threshold, there are a few classifications like normal, mosaic abnormal, this gives us information about the amount of unhealthy DNA. Normal is if aneuploid DNA in a single biopsy is less than 20%, mosaic is if the aneuploid DNA in this single biopsy is between 20-30% and aneuploid if the aneuploid DNA is more than 80%.
For women with exhausted oocytes reserve, the probability of fulfilling the desire to have a child with their own oocytes is very difficult, so egg donation is the option that can help achieve this goal in the end. It’s a treatment with a very high success rate, the pregnancy rates are around 75% with the first attempt at our clinic (IVF-Life). The reason for that is that egg donors are very young and they have the best oocyte quality. We do some tests before the treatment and before selecting a donor, a mapping of their own chromosomes that allow us to see if they have a higher tendency of producing unhealthy embryos. This factor allows us to have very high success rates, there is the success rate of the time spawn between 20- 25 years old
One of the publications from 2007 from the UK shows how the live birth rate decreases with the advanced maternal age of the eggs and therefore conclude how important healthy eggs are for success. We can see how extremely difficult it is to have success with your own eggs between the age of 44-46.
Regarding PGT-A testing in another publication from 2016 performed in the US, we can see that in certain groups PGT-A testing is beneficial. Patients of advanced reproductive age and a certain collective may benefit from PGT-A.
We can see that at a young age, the age of the donors is between 20-25, we have no significant advantage when we perform PGT-A testing, it’s rather the same when PGT-A testing is performed, you see that the live birth rate is high, so women have the success rate of the donors.
PGT-A testing is rather a matter of debate. For example, mosaicism is where a certain amount of DNA in the cell is not okay, it’s frequently found in pre-implantation stage embryos, and it seems that it represents a normal physiological finding at those stages. Chromosomally abnormal embryos may self-correct downstream, this explains the persistence of chromosomally abnormal cells in the placentas of healthy babies.
Another reason why it is criticized is that the average 5-7 cells of the trophectoderm biopsy that we perform cannot define the state of an embryo for 100%. Something that we are also not 100% sure about is the impact of damage that is caused by a biopsy, human embryos are sensitive to manipulation and biopsy.
Several case reports are showing that embryos tested as mosaic but in some cases also as aneuploid resulted in healthy babies. We have a high number of false-positive rates, which means that this test can show us that the embryo is unhealthy or not suited for a transfer, but in reality, it’s suited for a transfer. Consequently, one must conclude that many false-positive embryos are either not used in a treatment maintaining clear preservation or even get discarded, therefore, it’s also an ethical problem.
There is also a STAR trial, which stands for a Single Embryo Transfer of aneuploid embryo, it was a multicentric study including 4 countries and many centres. It was one of the largest studies undertaken, and it included 650 subjects. They were randomized, the primary outcome of the study was the ongoing pregnancy rate after the 20th week of pregnancy. It was found that the ongoing survival rate was not a lot higher regardless if PGT-A testing was performed or not. However, as shown on the slide, a certain patient group would benefit out of it, it was the group of 35 to 40 because the ongoing live birth rate was much higher. When PGT-A testing was performed at a younger age, so we’re talking about the egg donor, it didn’t make such a big difference at all.
It’s very important to see the big picture. PGT-A testing offers benefits when it is used properly, however, we mustn’t forget that not all couples will benefit from it. The patient should have an increased reproductive age and produce multiple embryos.
- Questions and Answers
We must take into account that every time it must be an individual decision. All the factors of the couple matter, for example, if the couple faced multiple implantation failures, miscarriages, in such cases, patients could benefit from PGT-A testing. Patients who undergo egg donation need to look at the live birth rate of the donor, so they have the live birth rate of a 20-25-year-old, PGT-A testing doesn’t make a big difference, and it could be most likely counterproductive in the end. It’s because of false-positive results, and the ethical dilemma is also a matter of debate. One exception could be where the Karyotype of the husband or some findings could lead to a higher tendency of producing unhealthy embryos.
As I said before, egg donation gives us a very high success rate on its own, so there is no significant benefit out of PGT-A testing with egg donors.
If we have a male factor, it’s not always possible to recognize a microdeletion in the karyotype. Some minor abnormalities that seem to be minor can lead to a higher tendency of producing unhealthy sperm/ eggs. In such situations, yes, PGT-A testing could help us a bit.