Preimplantation Genetic Testing (PGT) is an approach many waiting couples are now adopting to record a successful IVF (In Vitro Fertilization). It helps in achieving family balancing and bringing-forth healthy children. Speaking on the efficiency of the PGT, Fertility expert and MD, Nordica Fertility Center, Dr. Abayomi Ajayi, during a media chat gave a detailed insight into how the works and why couples who are waiting on the lord should go for PGT. Below are what he said:
Preimplantation Genetic Testing are tests used in assisting reproduction. As its name suggests, these are tests that are done in embryos through IVF to test for their genetic competency before the transfer is done. It is only after transfer that you can have the implantation so that is why they are called pre-implantation genetic testing.
There are about 3 types of tests that we can do, one is what we call PGTA or PGT Aneuploidies. This looks essentially at the number of the chromosomes. Now we have seen that the majority of the failure that happens in IVF and miscarriages comes as a result of error in division of the cells. Now, this is what I mean; you know in IVF, we are able to get 15, 20 eggs, sometimes more than that unlike when the nature that is usually one egg that happens in a month but there is also now a limiting factor to getting 15, 20 verified eggs. The problem is that it’s not all of them that can become babies and that is one of the reasons why we are not having a 100% in IVF because when this divides for an organism to be formed. For example, let us look at the human organism, the sperm and the egg come together as one cell each and then they unite. After fertilization, it becomes two, four cells. It starts dividing and as this division is taking place, sometimes there are errors in this division whether it’s IVF or on the bed, the same things happen and that is why it is not every time that a woman gets pregnant that she carries to bed. Even naturally, we know that in nature about 11-20% of pregnancies are miscarried but in the IVF lab, because we have so many more; we know that about 25% of the embryos that we produce in the laboratories cannot become babies. That is the technology itself. It can even be worse if your laboratory is not working very well. But if your laboratory is working top notch, about 70-75% of your embryos cannot become babies. Why this is so is because of these errors that happen during the time that the cells are being divided. So that’s why you have an abnormal number of chromosomes. Let us understand what I am talking about a little bit, when I am talking about genetics, we talk about chromosomes, we know that we are made up of cells and the cells because they are living cells, they have nucleus and in the nucleus is where all the activities take place. In the human cell, DNA is the component that is responsible for us to transfer our genetic material to our offspring. This DNA is combined with protein and they are beautifully woven into some structures we call chromosomes in the nucleus. Inside these chromosomes are the genes, what we first look at is the sign, for an embryo, what happens is that during the cell division if there is a mistake instead of the 23 pairs of chromosomes that we see. I always liken it to a shelf that has 23 layers and the third layer is the sex chromosomes that is where you see if it is a boy or a girl and I always say that because a woman only has XX chromosomes each time.
To determine the sex of the baby, all that the woman can present is the X chromosome but for the man, he has XY chromosomes so it is either the man is presenting another X chromosome or another Y chromosome. That is why we say it is the man who determines the sex of the baby because the woman does not have any other chromosome other than the X chromosome. So, if you go back to that cell concept, there are 23 layers but they are two group on each layer one on the left and one on the right whichever one you like whether left or right comes from the woman and the second one comes from the man and this is what unites to form an organism. But the thing is that, from that two cells, to four cells, to eight cells, it is supposed to be uniformly dividing but sometimes some problems just arise naturally. We can now see mistakes happening in that division and once nature senses that mistake. And that is why I say reproduction is not only efficient but very specific. And that is why we do not have babies with two heads working around the whole place because the moment nature senses the mistake, it kills that embryo. And that is why you do not get pregnant or sometimes you have a miscarriage. So, we have seen that the majority of the failures we have and the miscarriages that we have is because the embryos that we have transferred have these errors. So, that is the basis of that first test that we call PGT Aid or PGT-A test or PGT Aneuploidy test. Aneuploidy means an abnormal number of chromosomes that we can easily see. But do not forget that while we are looking at the number of chromosomes, another thing that we see is the sex of the baby, the last set of chromosomes will tell you whether it is XY or XX. So that is for the first test.
The second test is what we call PGT-SR which means PGT Structural Rearrangement. Do not forget the first one, the aneuploidy is about numbers. This now is about structural rearrangement. For example, one of the chromosomes might actually be cut into two, that might be the accident that happened but usually those are the inherited ones. Maybe the father’s own is cut into two sometimes one of the chromosomes is upside down. Sometimes, we call it aversion. Sometimes, we call it translocation. So, the one that is supposed to be on layer 2 is on layer 3. We call that structural rearrangement. Usually, that is also part of things that can be inherited. Don’t forget most of the numbers are not because it is inherited. It’s because there has been an error in the number during division.
The third is the PGT-M which is a monogenic disorder. It is a little bit more complex. This is what we used to call PGD because it is more of diagnosis not screening. In PGT-M, what we do is that; we now open that book on the shelf. For example, if we want to look at shelf 2, we open it. We have learnt so much about DNA. We know that DNA is boring, it just uses four alphabets to write but sometimes errors occur in these 4 alphabets. So, sometimes it uses ACT and ACTH. Sometimes, it wants to write ACT and it writes CTA, that is an error that is like what happens in sickle cell disease, it wants to use a particular amino acid but another one comes and once that error starts, the body continues to manufacture that error but we are able to see when it is only one and that is why it is called monogenic disease. It’s only one amino acid that is the problem in sickle cell disease and so we are able to see it with PGT-M and so these are the 3 implantations testing that we do.
Who are the people that will need this and why do we need to want to see their errors and that is why we always talk about age because the incidence of the errors increases by the age of the woman. Let us put it this way, studies have been done to show that we have 5 embryos from women who are below 35, about 50% of the embryos will be able to become babies so when we talk about that 75, we are talking about the average of all ages but it is only women below 35. 50% of their embryos can become babies but it is because it is not only under 35 women that do IVF. By the time you come to ages 40 and above, it is only about 15% of the embryos. In fact for 42 and above, less than 10% of them can become babies and that is why the doctor is always talking about age and IVF success because this is what happens naturally and why we are seeing it on a higher scale and now instead of one egg which normally would have done the job we now have ten eggs that we are using to do these same things in the laboratory so that’s why we have increase as it were, if all the women we are treating were below 35 years old then that percentage goes down automatically, does that answer your question? so it is a natural thing not because of the technology, it is what happens naturally.
Who are the people who require PGT? The first set of people are women above 37 because with them, the number of embryos that cannot become babies has suddenly increased from the 50% that we spoke about women in their less than 35, for their own, it has become 60 so they need to look at which of the embryos can we use. Number 2, people who have had a history of an abnormal baby before either a family thing or directly. Thirdly, is recurrent miscarriages people who have had recurrent miscarriages either naturally or through IVF. There is a fourth group that people are not talking about so much because they are looking at them and these are people who have very severe factor infertility when the sperm is very bad because we have seen that when the sperm is very bad the number of abnormal sperm also increases so these are the people who will need PGT.
The question maybe now is how is PGT done? Well, like we said it has to be through IVF, so we must form embryos, many years ago, we used to use the three embryos because we take samples from the embryos and see their genetic competence but this method was not very efficient, there were a lot of studies that douched this. Right now we use lastosis, so it is either the five or the six embryos and there is no difference in the result whether it is five or is six and the embryologists are trained to take this biosis from the embryo without harming the embryo because while they change is from the part of the embryo where the placenta forms so they cannot accidentally change the nose of the baby or the mouth of the baby. So it is the area where the placenta is from that is why they are taking the samples from and they take about a few cells which is supposed to be representative of the embryo, I chose my words properly because sometimes it is not, they now use that to analyse the embryo to see the genetic composition and of course the sex of the embryo. And then depends on what we are screening for, now that we are having quite a number of AS people getting married in Nigeria too we were screening for genetic disorder like sickle cell diseases also we are doing and family balancing using PGT as well like I told you, and then we just transferred the embryos that either for example, at the desired gender if it is sickle cell disease we only transfer gender that are not affected by the disease. Now, there are other diseases that are not affected in fact about 600 diseases that the pattern has been discovered you know what this is all about is that we can do the genome of the human being that is all the DNA in a human being can be arranged and that is becoming much more cheaper I think it’s probably about 200, 300$ from about 10,000$ when it first started but it is because you know technology over time becomes cheaper. So, it has been able to see the sequence of things. For example, what is the sequence of albinism? What is the sequence of congenital blindness and then we can see that and say no, these embryos are affected for families.
The good thing about this is that because we have been able to screen these embryos to see the ones that are genetically competent apart from looking for diseases. The ones that you are going to transfer have the correct numbers of chromosomes. Success rate of IVF now increases because of that. Some people have reported 50-70% are cycled of selected embryos but some people are saying it is not that high but whatever it is, there is no doubt that time for pregnancy is reduced when you are using selected embryos instead of you. You know the problem most of the time before the problem is that you select two embryos by, you know what we do normally in the IVF and the two of them don’t have genetic competence that the number of chromosomes in them is wrong and so either it does not take at all or it takes miscarriage but in these cases when the embryos are selected, the chances that it will take is higher. The chances that it will be miscarried is lower. So those are the advantages of doing PGT.
