Watch the recording of the Online Patient Meeting with Jose Luis Pablo Franco, M.Sc., IVF Laboratory Director at Fertility Madrid & ART Vitoria, who is answering the most common questions on embryo quality and PGT-A testing.
Jose Luis Pablo Franco presented an embryo of very good quality from day-1 to day-5 during his presentation. The first picture shows an embryo in day-0 when the gametes are put together, the sperm and the oocytes with conventional IVF or ICSI. Then during day-1, the embryologists check fertilization of that oocyte, they want to see which ones are well fertilized. On day-2 of embryo development, the embryo is divided, it’s a four-cell stage embryo. On day-3, there are 8-10 cells, day-4 is already called a morula stage embryo. It doesn’t give too much information, therefore, embryologists don’t take this one too much into account. The last one is called the blastocyst stage, it collapses and then develops. Together with some enzymes, it will get rid of the zona pellucida. Zona pellucida is a layer that protects the embryo during those first days, but in the end, it will disintegrate.
Day-3 versus day-5 embryo
The day-3 embryo has different features, Jose explained that we see the number of cells, the symmetry of those cells, either even or uneven. We see if they have one nucleus or more per cell, it’s better to have just one nucleus per cell. Another feature could be fragmentation, which occurs when a cell divides into two cells. The cell leaves a part of that cytoplasm outside, and if you have a lot of this cytoplasm outside, this can harm the embryo, it won’t let the embryo develop properly. These are the main features that are taken into account when we speak about the day-3 embryo.
When we’re talking about day-5, the blastocyst stage, there are two parts to differentiate. The first one is the inner cell mass, which has to be of optimal size and shape. The size is a cumulus of compacted cells, and the inner cell mass is going to become an embryo in the future.
Then we have to take a look at the rest of the cells, so the inner cell layer has to have a lot of even cells. Based on these two parts, the embryologists will be able to grade the embryos as A, B, C or D.
Grade A and B are the best embryos for transfer. Grade B has a little more fragmentation, and if you take a look at the blastocyst, you will see that the inner cell mass is not that big, and the trophectoderm doesn’t have as many cells. If you take a look at grade C, there is even more fragmentation, and grade D embryos are not used.
When we’re talking about day-3 embryos, we cannot differentiate between cells and fragmentation. If you see the blastocyst, you cannot differentiate the inner cell mass and the trophectoderm.
Time-lapse technology (TLT)
It’s an incubator that takes a picture of each embryo every five minutes. That means we don’t need to take the embryos out of the incubator to check and take them under the microscope. Embryos are always in stable conditions, such as temperature, CO2, O2, that need to be controlled for good embryo development. Thanks to incubators, we also have a lot of information to try to select the best embryo for transfer, the embryo with the best chance to implant.
Fertility rates vs. miscarriages rates
If you look at fertility and the miscarriage rates in your 40s, the possibility of pregnancy is going down fast, while the chance of miscarriage is going up quickly. When we are talking about morphology, we need to remember that if we have a grade A blastocyst, and you’re 30, and then you have a grade A blastocyst when you are 42, the pregnancy rates are not the same. The morphology is the same, but we don’t know what is going on inside this blastocyst. This can be checked with PGT-A (Preimplantation Genetic Testing for Aneuploidies).
PGT-A (Preimplantation Genetic Testing for Aneuploidies) — indications
As Jose mentioned before, we need to take into account the morphology of the embryo, but this won’t tell us anything about what’s going on inside those embryos. Therefore, this is a technique that can tell us that. This genetic test can identify embryos that have the normal number of chromosomes, which means they are euploid and those that have abnormal cells, called aneuploids. It’s not possible to fix those aneuploidies, the only thing we can do is to check the embryos that we have.
PGT-A is usually indicated for women who had more than 3 miscarriages, with previous implantation failures, which means they have had 4 or 5 good quality embryos transferred, but they didn’t get pregnant. Maternal age is also important. When you are 39 and above, you have a higher chance of miscarriage. An abnormal FISH test is also a good indication for PGT-A, this test will show us whether the chromosomal composition of the sperm is normal.
Another test that we often use is PGT-M (Preimplantation Genetic Testing for Monogenic Disorders). It is recommended if any of the intended parents is a carrier of disorders such as Steinert myotonic dystrophy, Duchenne muscular dystrophy, Huntington’s disease, and fragile X syndrome. This technique is used to analyse the embryos to prevent offspring from the disease their parents have.
PGT-M & Day-3
Biopsy for PGT‐M is usually performed at day 3 of cleavage‐stage embryo development when the embryo is at the six to eight‐cell stage. On day-3, we choose the cell that we want to take out. We select the one with one nucleus, we make a hole with a laser, and we take that cell out. Sometimes, two cells are taken because, in this case, one cell was for PGT-A, and one cell was for PGT-M. It’s possible to do both. If a patient is in her 40s and has a monogenic disease, we can analyse the embryos for that disease, and after that, we’re going to check the chromosomes, so we can do both at the same time.
PGT-A & Day-5
During day-5 blastocyst biopsy, we make another hole with the laser. We wait until the trophectoderm comes out a bit, and we aspirate one cell, we continue to aspirate it and perform two pulses of laser to make the blastocyst shrink. When it is shrinking, it’s easier to take out more cells, it’s best to take around six or eight cells from that blastocyst, then it is vitrified, and sent to the genetic lab. The results are ready in about more or less one week.