Lots of patients know that the commonest cause of IVF failure is a failure of the embryo to implant. We also know that the commonest reason for implantation failure is a genetic defect in the embryo. This is why it seems very tempting to do pre-implantation genetic screening ( PGS, aka as PGD = preimplantation genetic diagnosis) and PDT = preimplantation genetic testing) for all IVF patients, so that you can select the genetically normal embryos . This should increase the chances of implantation and reduce IVF failure. After all, what’s the point of transferring a genetically abnormal embryo back into the uterus ? It will just fail to implant, or even worse , end up in a miscarriage.
This makes logical sense, but unfortunately , in real life , biology is far more complicated. I think we need to remember that when we’re doing PGS , we’re really not doing genetic screening; we’re really just doing chromosomal screening, so a better name really would have been pre-implantation chromosome screening or PCS.
Why is this important ?
All these tests ( for example, CCS and NGS) only allow us to make sure that the cell has a normal number of chromosomes. This means we can make sure it is euploid, so that we can screen out which embryos are aneuploid ( they have an abnormal number of chromosomes) . Aneuploidy is an important cause of failure of implantation as well as miscarriages, but we also need to remember that counting the number of chromosomes is not enough if we want to identify genetically normal embryos. After all, there are over 30,000 genes , and there are only 23 pairs of chromosomes. This means that even though an embryo may appear to be normal on a PGS, this does not mean that it is genetically normal. Thus, a lot of PGS normal embryos will have a normal chromosomal complement, but they will still have lethal genetic defects that prevent them from implanting.
Unfortunately , most patients don’t understand this difference. When they end up spending a lot of money in order to transfer a PGS-normal embryo , and then still end up with a failed IVF cycle or a miscarriage, they’re obviously very bitter and angry and feel they’ve been misled. This can create a lot of dissatisfaction.
Many patients come to us and ask that we do PGS/CCS for them. Typically, these are older women or those who have had failed IVF cycles elsewhere. They have read about this new technique online, and want us to do it for them, because it is supposed to improve IVF success rates.
There is a good reason why PGS/CCS is so appealing. It allows us to screen embryos , so that we can selectively transfer only the genetically normal embryos. Isn’t it common sense that doing so will improve IVF success rates ? And since it’s the newest technology around, it’s being marketed very aggressively and cleverly !
Logically, we should be very happy to do so ( because we can charge more for these additional services). However, as professionals we also need to explain to them that while PGS will help us make more money, it will not help to improve their chances of success.
Sadly, most other IVF clinics do not bother to do so . And if a patient wants a new technology to be used for them, and is willing to pay for it, then why not pander to their request and comply ? It takes too much time and effort to say No to a patient’s request – and it’s hard to say No when you are turning away additional income. It’s true that we lose these patients to other clinics, but other than educating them, there’s nothing else we can do about this.
Because we are well off and very busy, we are in the fortunate position of being able to afford to say No when we don’t think the inappropriate overuse of technology is in the patient’s best interests !
If you want to read why PGS does not help, please read the article, “Improved” Preimplantation Genetic Screening (PGS) Not Proven to Increase IVF Success Rates, at http://www.digitaljournal.com/pr/1801245
https://www.hfea.gov.uk/treatments/treatment-add-ons/pre-implantation-genetic-testing-for-aneuploidy-pgt-a/ h from the HFEA, UK, as more information why you should not allow your doctor to do PGT for you
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