In this webinar, Vladimiro Silva
, PharmD, Embryologist, Founder & IVF Lab Director at Ferticentro, Coimbra, Portugal, presented 3 real-life cases where embryo biopsy was necessary to achieve a pregnancy and a healthy baby.
First, Dr Silva started by stating that genetics starts with counselling and, roughly speaking, testing the embryos. Genetics is also about making informed decisions about your embryos. If you are a carrier of a genetic disease, you have to live with that, if you are a woman older than 39, your eggs will have a certain risk of being aneuploid or having genetic abnormalities, and we cannot do anything about it. However, we do know whether those problems exist or not, and we have the power to decide what can be done with that information.
IVF & genetics – what’s the purpose
What’s the point of performing genetic testing? IVF is very useful to prevent the transmission of genetic diseases, it is also used to screen for potential genetic issues, some of them are age-related, and some of them are not. We are born with them, and it is also used to find HLA compatible embryos in very special cases, for example, we’re talking about compatibility to do bone marrow transplantations, and IVF can also help us with that.
There are 3 types of genetic tests that we can do in IVF:
- Preimplantation Genetic Test for Monogenic disease (PGT-M), if you are a carrier of a certain disease, such as Huntington’s disease, neurofibromatosis, or if your partner is also a carrier in the case of recessive diseases or if it is an autosomal dominant disease, this means that if you are a carrier, you will always have the disease you are at risk, and you can resource to IVF to avoid passing that disease to your child
- Preimplantation Genetic Test for Aneuploidies (PGT-A)
- Preimplantation Genetic Test for Structural Rearrangements (PGT-A), sometimes we are a carrier of a genetic abnormality in our karyotype in the number of chromosomes that we have, but that change is balanced, so we don’t have any disease, we live a completely normal life because we have all the DNA that we require to do that but when we are forming gametes, sperm, or eggs in the case of women there could be problems
- Preimplantation Genetic Test for HLA compatibility
PGT-A (formerly PGS)
It is a genetic test that we do on embryos to screen for numerical chromosomal abnormalities. We all have 46 chromosomes, and sometimes either because of the egg or the sperm, embryos can have an extra chromosome or a missing chromosome, this is what we call an aneuploidy which means embryos with the wrong number of chromosomes. If we have embryos with the wrong number of chromosomes, those embryos will most likely fail to implant, and so we will have a negative result, or if they implant, they can lead to a miscarriage. However, in some situations, if implantation is successful, it can lead to the birth of a handicapped child or a child with a genetic condition. When we have a chromosomally normal embryo, we call it a euploid embryo, and we know, for a fact, that these embryos are more likely to lead to a successful pregnancy. PGT-A is done with The Next Generation Sequencing method (NGS), it’s used all over the world these days, and this allows us to analyse all 24 chromosomes because we have 23 pairs, so a total of 46. There are 24 different types of chromosomes, but only 23 pairs, so these chromosomal abnormalities are detected before embryo transfer. We get the eggs, we fertilize them in the lab, we create embryos, and we cultivate the embryos until day-5 or day-6, in some rare cases, we might even take them to day-7, and then we make a small hole in the embryo, we take some cells out, and we test those cells, we freeze the embryo, and we wait for the result of those tests.
This allows patients to make informed decisions about their treatment, this is not about making your embryos better, it’s about getting information and the capacity to select the best embryo. If, for example, none of your embryos is viable, you might think, or you might consider egg donation, or you won’t lose time transferring lots and lots of embryos.
PGT-A is related to maternal age, on the graphic shown, until above the age of 35, the probability of having abnormal embryos spikes, and it ends up at 76% at the age of 43 or 44 years old. This is why egg donation is such a good alternative for many patients because we know that egg donors are less than 35 years old, and so that’s when the risk of having a chromosomal abnormality is lower. It’s important to keep in mind that chromosomal abnormalities can also come from the sperm, but in statistical terms, this is more associated with the maternal age and the quality of the egg.
Some data from Igenomix show the results of IVF with PGT-A where the implantation rates are relatively steady across all age groups, this is the age lower than 35 below 42 years old, even though it goes a bit down, the differences are not that significant. However, if you look at IVF without PGT-A, you will see the natural pregnancy rate go down. It is because we also have to think about the uterus and the endometrium and those unselected embryos. PGT-A doesn’t improve your chance of getting a baby, it just helps us identify the most viable embryos. The delivery rates follow the same trend, and miscarriage rates follow the exact opposite trend. When we are doing PGT-A, we’re less likely to have a miscarriage because we identify embryos with genetic abnormalities, when we’re not doing it, we are risking the transfer of embryos with genetic abnormalities, so this is another reason to do it.
The risk is very age-related, for example, when we are talking about an egg donation case, since the donors all belong to this group, there is no difference. It doesn’t make sense to do PGT-A in egg donation cases.
PGT-M (formerly PGD)
It is used to avoid the chance of having a child with an inherited genetic disorder. The process looks the same as in PGT-A, we create the embryos in the lab, we analyse them before the embryo transfer, and we identified those who carry the alternate disease-causing gene. This is intended for patients who are known to carry serious genetic diseases (either autosomal dominant or recessive). It’s a custom-designed test for every patient. There are thousands or hundreds of variations for every disease, so in genetic diseases, it’s more or less the same. For example, for cystic fibrosis alone, there are more than 1 500 known mutations, so even though we have to identify those mutations, then there are still inter-patient differences that we have to identify to prepare for the test. All patients have to do an initial test this is what we call the pre-PGT test, this is used to prepare the test, then we create the embryos, we take the cells out of the embryo, we freeze the embryo, we wait for the PGT results, we send those cells to the genetics lab, and then they will tell us whether that embryo is a carrier, for example, of the Huntington’s disease, Neurofibromatosis, Cystic fibrosis, spinal muscular, atrophy, etc.
PGT-SR (formerly PGD)
It is intended for patients who are known to carry karyotype abnormalities such as lesions, duplications, and inversions. Sometimes a part of the chromosome is swiped with another chromosome, and so in the gametes that are being built, it causes an imbalance in forming the spermatozoa and eggs in the case of women. This can be inherited, or it may occur spontaneously. This is a karyotype abnormality that affects 1 in every 500 people, it doesn’t cause any problems to the person that carries this abnormality, they normally find it when they are trying to have a baby because they’re getting negative results, and they don’t know why so we do the karyotype test and we find that.
One of the examples is a translocation between chromosome 14 and chromosome 7. A part of the 14 chromosomes is on chromosome 7, and a part of the 7 is on chromosome 14. That person has all the DNA necessary to have a normal healthy life and doesn’t have any issues, however, when a woman is creating her eggs we’re only transmitting 1 chromosome from every pair, and so if we transfer the wrong chromosome to the egg, the only way to balance it is if the 14 has a part of the 7 is also transmitted. If she passes the 7 with the part of the 14 and the normal 14, then there is an imbalance because there will be too much of the 14 chromosomes. This can cause either miscarriages or negative pregnancy results, or maybe the birth of a child with genetic abnormalities.
Preimplantation Genetic Test for HLA compatibility
In some situations, for example, in children with some very severe diseases, the only way to find the only solution and treat them is by finding a compatible sibling, a compatible bone marrow donor, and sometimes a compatible bone donor is very hard to find. Quite often, the only solution is to have a genetically compatible sibling. These situations always have to be approved by the national IVF authorities, those are ethically complex cases but they allow us to save the lives of children that otherwise will have no chance of survival.
Genetic issues – real-life cases
The first case presented a 42-years-old single woman, she never tried for a pregnancy, she had a normal BMI, and she decided to have a child with an anonymous sperm number.
- a 42-year-old single woman, no previous pregnancy, high AMH level for her age, using an anonymous sperm donor
After evaluating her ovarian reserve, we got this astonishing value of 5.1 ng/mL, her FSH and LH were very well balanced, so her ovaries were working very well. We did an aggressive stimulation because we knew that from a normal point of view, we had everything we could dream of, however, there was the age factor, and it’s impossible to take the time to go backwards. We needed a lot of eggs, and the stimulation wasn’t that wonderful, we only got 9 eggs which are great in every age group, but from AMH of 5.1 ng/mL, we could expect 20 eggs or so. We got two day-6 blastocysts, we performed PGT-A, and we found that 1 of the embryos was aneuploid which means it had either an extra or a missing chromosome, another blastocyst was a mosaic embryo with 30% of the cells were abnormal.
We have to remember that when we do PGT-A, we’re only taking a group of cells from the embryo, normally 5 or 6 cells because we work with day-5 five or day-6 blastocysts. Sometimes they can or can’t be representative of the rest of the embryo, we can’t test all the cells of the embryo because otherwise, we would lose the embryo. The theory behind PGT-A is that those 5 or 6 cells are representative of the rest of the embryo. In this group of cells, 30% of them were abnormal, and 70% of them were normal. After discussing with the patient and talking to the genetician she decided to transfer that mosaic embryo, and luckily she got a healthy child, she did the amniocentesis, and the karyotype of the child and everything was okay. She now has a baby girl with a normal karyotype.
This is a typical case of a woman for whom PGT-A was very important because 1 of the embryos wasn’t viable. The fact that she did PGT-A led her to make an informed decision about mosaicism and also while doing the prenatal diagnosis procedure, the doctors knew that they had to do an amniocentesis because of the PGT-A result.
Another case presented a single woman in her 40s, her BMI was 25, so it was borderline normal, and she was a carrier of a genetic disease, it was an autosomal genetic disease, which means that she had a 50% risk of transmitting that disease to her child. We had to do the pre-PGT test, we had to test her and the sperm donor. We always keep DNA from our donors, we sent that DNA to the genetics lab to do the pre-PGT test.
- a 40-year-old single woman, a carrier of genetic disease (ADPKD) – autosomal dominant: 50% risk of transmission
We started the stimulation with HMG of 375 UI a day, which is considered to be an aggressive protocol, and we got 5 eggs. From these 5 eggs, it was very likely that we wouldn’t have any viable embryos. Therefore, we did a second stimulation, we’ve frozen these eggs, and the result was different, we changed the protocol to the gonadotrophin, and the reaction was a lot better. We got 29 eggs, it was a completely amazing result for a 40-year-old patient. We’ve fertilized all of the 34 eggs, we warmed 5 that have been collected initially, and we got 22 developing embryos and 13 blastocysts. We did PGT-M, from those 13, 7 were not carriers of the genetic disease, and then we did PGT-A to test it because sometimes an embryo is not a carrier of the monogenic disease, but it can be, for example, trisomy 21. We did PGT-A on the 7 blastocysts that were not carriers of the genetic mutation, and 6 of them were euploid, which was also an amazing result. We transferred one of them, and there was a birth of a healthy child, and we still have 5 blastocysts frozen.
The last case presented a 25-year-old woman, with a normal BMI, she already had a child, and her child had a severe haematological disease according to the paediatrician’s team that was taking care of her daughter, the only solution to treat the existing child will be through a bone marrow transplant from a compatible donor. They were waiting for 3 years to find a compatible donor, but it didn’t happen. They knew that the theoretical probability of finding a compatible donor in a sibling was 20%, so they submitted an authorization request to the Portuguese IVF authority (CNPMA), which authorized treatment.
- a 25-year-old woman with a husband, and 1 child with severe haematological disease; tried to find a compatible donor without success
We did the treatment to search for HLA compatibility selection, so it’s kind of a specialized form of PGT-M. We did the first ovarian stimulation, and we’ve we had 23 eggs, from this 23, we were expecting 20%, theoretically speaking, we would have 4 eggs that could be compatible, but we have to play also with the pregnancy rate, even though the patient was 25 years old, we could aspirate to have 50-60% so it was narrow and we would depend on luck. We decided to freeze all of these eggs, and then we did a second ovarian stimulation, and we got 33 more eggs, so we ended up fertilizing 56 between the fresh and the frozen, at the end of everything, we had 14 blastocysts, and we did the PGT-M for HLA compatibility, we got 3 compatible blastocysts. From those 3, we did PGT-A to see if they had the right number of chromosomes, and they were all euploid which was amazing, then we did the first embryo transfer, and the result was negative. We got very worried because there could be something else, and we only had 2 additional embryos out of 56 eggs, and it was a lot for the patient. We studied her endometrium, and we ended up finding that her endometrium was only receptive at 14.5 hours of progesterone which is what we call a misplacement of the window of implantation, so we did the frozen embryo transfer respecting the indications from the ERA test and we had the birth of a healthy HLA compatible child, and so hopefully everything will go well for this family.