During this event, Dr José Félix García España, Medical Director of UR El Ángel, explained how Preimplantation Genetic Diagnosis without the need for invasive biopsies works and its current status.
First of all, if we talk about non-invasive or invasive PGT-A, we need to know what chromosomes are and what a karyotype is.
We can identify euploid embryos, indicating normal chromosomes. For instance, consider a typical male: 22 pairs of chromosomes plus the sex chromosomes X and Y. Similarly, a typical female possesses 22 pairs of chromosomes along with the sex chromosomes X and X. Now, contrast this with an aneuploid embryo, such as one with Down syndrome. In this case, observe that in position 23, there is a deviation from the usual pair – instead of two chromosomes, there are three. This abnormality is characteristic of Down syndrome embryos.
In the past, our methodology, illustrated in the second point, involved performing invasive procedures years ago. Specifically, we utilized a biopsy technique during the early stage when the embryo consisted of eight cells.
This method, however, had limitations. It lacked precision because, during the biopsy, we could only extract a single cell. Attempting to obtain more cells posed a risk to the embryo’s viability; obtaining additional cells could potentially lead to the embryo’s demise. Consequently, relying on just one cell for analysis proved insufficient and non-representative of the overall embryo.
In the current scenario, the invasive biopsy is conducted at the blastocyst stage, typically on day six or day five of the embryo’s development. This stage is characterized by a considerable number of cells within the embryo. During this procedure, we can successfully extract a substantial group of cells, usually six to seven cells, enhancing the accuracy of our diagnostic process.
Looking at the graph, we can see on the first line, we see a line here, and then it’s very small, but here is chromosome number one and one, 2, 3, 4, 5, etc., chromosome 22 and the X and Y, and this is a normal, an euploid embryo. When they see that, they say, “Okay, we can transfer this embryo because it’s normal.” You see that all chromosomes in the line are at the same level except the Y, which is smaller has less weight, and comes down a little bit more.
Number two and number three, in red, are aneuploid. They are abnormal, and you can see here there is a defect in chromosomes in pair 22 or in the third one where we see problems in chromosome 15 in pair 15 and chromosome X as well. Therefore, these two embryos should be discarded and not be transferred.
What are the indications for invasive PGT-A? Advanced maternal age because the older the woman, knows that the quality of the eggs comes with more chromosomal alterations, and wants to know which one is normal because the probability of having a miscarriage or other abnormalities is high. Another indication is when we have a patient who has more than 2 miscarriages or failed implantation.
In situations where patients have experienced recurrent miscarriages or failed implantations, there is a demand to understand whether the cause lies within the embryos themselves, particularly due to abnormal chromosomes. Additionally, when there is an issue with male fertility, and the male contributes abnormal sperm, which could be due to factors like DNA fragmentation or alterations in DNA testing, it becomes crucial to explore and identify these factors.
Comparing niPGT-A to the invasive PGT-A, we see its effectiveness. In the graph represented by the yellow line, we observe that over time, the likelihood of achieving a successful pregnancy decreases. However, for women who haven’t undergone PGT-A, or any similar procedure under a different name, there is a significant difference. If a woman, especially one aged 42 or older, undergoes PGT-A through a biopsy of the embryo, and it turns out normal, her chances of pregnancy become equivalent to that of a 25-year-old. This underlines the successful resolution of the age factor in assisted reproductive techniques.
This non-invasive method employs an algorithm to categorize embryos based on their chromosomal characteristics. Group one represents embryos with a probability of more than 85% viability, while group two includes embryos with chromosome alterations, segmental or mosaicism, carrying a 40% probability of viability. The approach helps prioritize the transfer of embryos based on their likelihood of success. The algorithm plays a crucial role in identifying potential issues, such as chromosomal abnormalities, that may lead to conditions like Down syndrome or Edward syndrome.
In conclusion, while the non-invasive PGT-A boasts an 85% concordance with the highly accurate invasive method, it is not yet considered a diagnostic tool. Rather, it serves as a valuable biological marker, aiding in the early selection of embryos and preventing unnecessary transfers. The non-invasive approach allows for a more informed decision-making process, improving the chances of successful pregnancies.
Well, obviously, the danger of the invasive variant is that we may damage the embryo. I have to say that happens very, very rarely, but as we touch the embryo and take some cells out, some embryos may die. But there’s a principle in medicine never to cause harm, so if the technique was very bad, then we wouldn’t do it. Sometimes the embryo may get some damage at the time of doing it. How often does that complication occur? I don’t have the figures, but not very, very often. After having the biopsy, the embryos survive, but then the lab gives us a report that says that they didn’t get any conclusion because the cells they obtained didn’t divide properly or the chromosomes, and we have embryos without a diagnosis. That happens more often, and I suppose that problem may occur exactly the same as the non-invasive one, which is a technical problem in the lab, and they couldn’t see the chromosomes in that line that we saw before.
Well, because what we study with the invasive and with the noninvasive one is the karyotype of the embryo. Karyotype means to check the 46 chromosomes, the 22 pairs plus the sexual ones. If the line that we saw shows the karyotype in a line, there is no defect. If it shows a defect, like the number 22 not being in the line, it means that the karyotype is abnormal, and an abnormal karyotype means aneuploidy. Depending on the chromosomes where the line is disrupted, we can infer potential issues, like a defect on chromosome 13 indicating a risk of Patau syndrome. The karyotype in the embryo tells us if it’s normal (euploid) or abnormal (aneuploid), and we look at the karyotype in the embryo.
That is the discussion that we have with the patient. We advise the patient based on their specific situation—do they have repeated miscarriages or are they young with multiple embryos after IVF? For those with repeated miscarriages, we may advise the invasive test. For younger patients with many embryos, the non-invasive test may be recommended. It depends on the individual cases, and we tailor the approach accordingly. It’s a discussion we have to have with each patient, explaining the pros and cons of each option. In order to know what to choose at the end, they will decide, obviously, but under our advice.
I’m very tranked about that because I’m not going to decide what we’re going to transfer; it’s the geneticist. We have a very good department, and then I get the phone. Well, in the report, they say if I can, or I cannot transfer such an embryo.? It’s the responsibility of the geneticist who is going to make my life easy because they say, “Okay, this mosaic does not involve chromosome 21 or 13, as we said. First and second, in this mosaic, the percentage is low; it’s fine. Then you may transfer it in the last place.” So, I will be very happy because I got the report, the paper with the geneticist looking at the test is telling me what to do based on that; they know what chromosomes are involved. If there is any danger or there is the possibility of having an unhealthy baby with a problem, it will be discarded, and the percentage of mosaicism will be provided.
No, no, it’s not possible to do the fresh. We have to freeze the embryos because it might take a couple of weeks or so to get the result. Okay. However, nowadays, we freeze almost all embryos. It’s been a long time since we don’t have hyperstimulation syndrome, and we transfer all embryos. It’s not a policy of freezing all, but almost. Only the low-responded ones are transferred with fresh embryos. And also, I tell them, “Well, we freeze in the very best good way because we do it a lot. And then there is a 98% rate of survival of embryos after defrosting them. And also, if you have four embryos, you’re going to freeze three of them because we’re going to transfer just one.” So yes, almost. Also, I should say that in non-invasive PGT-A many times what we do is just the patient may decide. This is something else that I can tell the audience. Any patient may have four embryos, for example, frozen, and they say, “Well, doctor, now I changed my mind, and I would like to check it with a non-invasive one.” Fine. We’re going to defrost the embryos, and 6 hours later, we’re going to obtain cells or chromosomes from the medium and freeze the embryos again. Twice. And nothing happens, right? So this is normal practice, and we can do it and do the biopsy on day five and 12 hours later to freeze the embryos again and to obtain chromosomes or DNA.
