Answer from: Raúl Olivares, MD
PGS is a technique with high accuracy with the current technology that we are using NGS, we can offer our patients 99% efficiency in detecting abnormalities. It could not be as high as amniocentesis, and this is just because of the number of cells that we have to study. In a standard PGS, we are going to work with 3 to 5 cells. In a standard amniocentesis, we may get 15, 25, or 50. The more cells we have, the more reliable the result is going to be, but the difference is very low. As I’ve said, we offer 99% in PGS and 99.8% in amniocentesis. In comparison, if you do the PGS, what you are going to do is get the results before even the patients get pregnant, and if we do that, we are going to help the patients to avoid having, for example, to decide a termination if the amniocentesis is abnormal. Whenever there is an indication to carry out a genetic test, in our opinion, it’s much better to carry out PGS and avoid the pregnancy than let the patients get pregnant and end up with termination if the amniocentesis is abnormal.
Answer from: Maria José Mendiola, MD, MSc in Human Genetics, MSc in Science Communication, ObGyn
Answer from: Dimitra Christopikou, Clinical Laboratory Geneticist
This is lab specific. Each lab needs its own KPI and its own quality control. We all need to test the embryos that we detect as abnormal and also we need to follow up all the pregnancies to test misdiagnosis. There is no number there and this number depends on misdiagnosis of the inaccurate result and depends on each lab. This number cannot be one hundred percent. PGT-A/PGS is not a one 100%test which is why we always recommend double checking the results with prenatal testing which is a better genetic test, carried out either in the trophoblast stage at CVS or at amniocentesis. Either earlier in gestation or later on in the eighteenth week which is amniocentesis.
Answer from: Luca Gianaroli
Like any technology, the accuracy of the test has improved a lot over the years. Generally, we can say that the risk of misdiagnosis is limited to 1-2%. The major problem that we are encountering is that the embryos or the part of the biopsied embryo could not represent the internal results of the entire embryo.
At that stage of development, the embryo can be a so-called mosaic embryo. This means that a few cells of the mosaic embryo tell us one thing about the number of chromosomes; whilst the entire embryo actually gives a completely different image in terms of chromosomes. This is a risk that you have to take. It is probably why you could still have a misdiagnosis in some cases due to not picking up a group of cells that represent an entire embryo.
