Do fertility doctors recommend performing PGS on donor eggs?
Pre-Implantation Genetic Screening, more commonly known as 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. Because aneuploid embryos commonly don’t implant well (and even if they do, they can result in further complications), by simply selecting the right embryo to transfer pregnancy rates shoot up.
Aneuploid embryos are most commonly created due to defects in either the oocyte or sperm. As such, is it worth performing PGS testing on embryos created through egg donation? We asked three experts that very question – here’s what they had to say.
Our experts are:
- Dr. Natalia Szlarb, IVF Spain, Spain
- Dr. Harry Karpouzis, Pelargos IVF, Greece
- Dr. Blanca Paraíso, Clinica Tambre, Spain
Dr. Natalia Szlarb,
IVF Spain, Spain
Answer from Dr. Szlarb
In answer to the first question as to whether PGS is worth performing in egg donation cycles, we have to be aware that when we women are born, we have a certain amount and quality of eggs in our ovaries. The older we get, the worse the quality of eggs that develop so when we review the literature, it seems obvious that when we speak about egg donation cycles, the euploidy rate—meaning the number of genetically normal blastocysts, embryos on Day 5 of development in egg donation cycles depending on data—is between 60–80%. When we look at the cycles of women over 35 years old, 50% of the embryos which they generate are euploid whereas with 40-year-old women that figure drops to 20–30%. From our personal experience at IVF Spain—where of course we perform PGS in egg donation cycles, especially with the second donor when we want to have perfectly selected embryos and time to pregnancy as short as possible—we see that some donors in one cycle have 80% euploid embryos but the same donor in the following cycle might have only 1–2 euploid embryos. So, statistically the euploidy rate of egg donation cycles is still 60–80% but we have to bear in mind that in one cycle the euploidy rate could be 80% and in another cycle it might be 60%. Definitely, in selected cases when time is no longer in our favour and the patient wants to be pregnant as soon as possible, egg donation and PGS is the methodology of choice.
Dr. Harry Karpouzis,
Pelargos IVF, Greece
Answer from Dr. Karpouzis
Well, actually this is a very difficult question to answer. The way I would answer it is this: PGS definitely needs to be offered as an option but only after very thorough consultation so that the couple is aware of the existing evidence, which is actually not conclusive. Only after knowing everything about what PGS really offers, they 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, an embryo that is chromosomally normal—the chances are higher with PGS than if we hadn’t done PGS beforehand. So, actually, 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, 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 actually 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 one that is chromosomally normal and the chances are much better with PGS.
However, generally, if we take everything into consideration—the cost and all the other factors—in the end it is a decision that needs to be made by the couple regarding whether or not 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.
Dr. Blanca Paraíso,
Clinica Tambre, Spain
Answer from Dr. Paraíso
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 very 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.