Pre-Implantation Genetic Screening (PGS) is one of the most commonly used diagnostic tests in modern embryology. It allows fertility specialists to identify chromosomally correct embryos from those carrying defects. Aneuploid embryos don’t implant well (and even if they do, they can result in further complications). By selecting the right embryo to transfer, pregnancy rates shoot up. Aneuploid embryos are mostly created due to defects in either the oocyte or sperm. So, is it worth performing PGS testing on embryos created through egg donation?
Answer from: Harry Karpouzis, MD, MRCOG, DIUE Gynaecologist, Founder & Scientific Director Pelargos IVF Medical Group
Well, this is a very difficult question to answer. The way I would answer is this: PGS needs to be offered as an option, but only after a very thorough consultation so that the couple is aware of the existing evidence, which is not conclusive. Only after knowing everything about what PGS offer, you can decide if it’s worth doing or not. To be honest with you, chances of success are really good even without PGS if we carefully select the donors—young, between 24–30 years old, with a full karyotype analysis to determine if they have any family history of infertility. We can even perform a fragile X genetic test on them. If the selection is well-made, the chances can be good even without PGS. So, if we want to answer the question if PGS does increase the chances or not, yes, it does, but mainly it increases the chances of the embryo transfer via an embryo selected through PGS. This means that if, for example, we have 4 or 5 blastocysts, and we do PGS on all of them, we know that from the initial transfer—if we have managed to find a blastocyst, a chromosomally normal embryo—the chances are higher with PGS than if we hadn’t done PGS beforehand. So, PGS makes it quicker as well. It makes a live birth happen faster. It reduces the chances of miscarriage to less than 6% because we know that if we transfer an embryo that does not have any chromosomal abnormalities, the chances of miscarriage are less than 6%. On the other hand, PGS is a procedure that costs a lot of money.
Also, there is evidence that even chromosomally imperfect embryos, the ones that have mosaicism—that is, normal and abnormal cells together—could result in pregnancy if we transfer them. They are embryos that would not be selected for transfer if we did PGS, but we would transfer them if we hadn’t done PGS. Additionally, PGS causes trauma to the embryo. Even if we do PGS on day 5—because nowadays we know that this gives the best results—it can cause trauma to the embryo, and we are not sure how exactly this will affect the chances of implantation. If we assess the total cumulative chances from fresh and frozen embryos coming from an initial egg collection without PGS, it would be equal to the chances of doing PGS because PGS would have possibly ruled out embryos that we would transfer if PGS hadn’t been done. Generally, it’s a complex issue, and to conclude, I would say that PGS needs to be advised if, for example, we have sperm problems and the karyotype of the male partner shows chromosome translocations or abnormalities then PGS needs to be done. Also, if we have had previous implantation failures or recurrent miscarriages with egg donation, PGS is recommended. Finally, I would say that if a couple specifies that they only want a single embryo transferred, this is also an indication for PGS because if we have a lot of embryos we can choose the chromosomally normal one, and the chances are much better with PGS.
However, if we consider everything—the cost and all the other factors—in the end, it is a decision that needs to be made by the couple regarding whether it is worth doing. If we have a lot of embryos, and if we do have a lot of blastocysts, the chances are always better with PGS. If we do not have a lot of blastocysts, maybe PGS will not play an important role because it means selection, and there is no selection if we only have two possible embryos to transfer one way or the other.
Answer from: Daniel Alexander, MUDr Gynaecologist, Physician Gennet
Well, there are situations when it’s worse but in general, the IVF egg donation is performed with young and completely examined egg donors. The egg donors have complete genetics and many times they have their own healthy children. So, if there is no genetic issue on the male side – on the partner’s side, there is no need for PGS screening in the egg donation cycle.
Answer from: Luca Gianaroli Gynaecologist, Scientific Director S.I.S.Me.R.
Most probably, it’s not as efficient as in other cases because we start from the assumption that the oocytes that are donated belong to young, healthy women. Many of them would give rise to healthy pregnancies, so they are not chromosomally abnormal. So, the diagnosis and the looking for chromosomal abnormalities is not so frequent in these oocytes.
We have to balance the cost of this technique with the benefits. Once the oocyte is donated, if the selection is made correctly, the chance of a miscarriage is minimal. The risk of not becoming pregnant is also minimal unless the recipient’s partner has a severe male factor. In this case, the male factor can contribute to aneuploidy which means chromosomally abnormal embryos. In this situation, it could be worthwhile to do a Preimplantation Genetic Testing for aneuploidy with a male factor indication.
Answer from: Blanca Paraíso, MD Gynaecologist, (Former Clinic) Fertility Specialist Clinica Tambre
In general, I would say that PGS diagnosis is not worthwhile in egg donation treatment. Why? Because chromosomal abnormalities of the embryos are normally due to an egg of advanced age. So, in this kind of treatment where we use eggs from young women, the expected percentage of embryos with aneuploidy, with chromosomal abnormalities, is very low. Of course, every case has to be taken individually—for example, if there’s a severe alteration in the spermiogram or other alterations of the spermatozoids are expected—and maybe PGS can offer a significant advantage. If a couple has had previous miscarriages or if a couple simply wants to undergo the procedure with more safety and try to achieve pregnancy earlier, of course, PGS will never have a negative impact. So, in general, PGS is not worthwhile but in particular cases, it’s always a good idea.