These two procedures have two common features and are also different. The common features are that they are applied on biopsied samples on pre implantation embryos either on day 3 or blastocyst states. But PGS checks on the number and structure of chromosomes whilst PGTA and PGD looks for monogenic disorders which checks for specific mutations in specific genes in the family. In the first one we are doing it to help women reduce miscarriages that are common after forty years of age due to chromosome abnormalities. In the second PGD or PGTM we are carrying it out to leave out inherited disorders and let the family have normal offspring.
PGT-A for aneuploidy is a test similar to tests women, who get pregnant naturally, take during pregnancy, like amniocentesis or chorionic villus sampling. It is a test in which all the chromosomes are analysed; they look for the normal number of chromosomes.
PGD for monogenic disorders, or PGD, for instance, is for diagnosing specific disorders. The parents or the potential parents already know that they are at risk of producing a baby affected by a specific genetic disorder. It could be cystic fibrosis, thalassemia, or any genetic disorder that we know can have a diagnosis at an embryo level.
The difference is that in one case we do a diagnosis for a specific disease. In the other one we remove the reproductive circuit from the embryos that cannot implant or go to term in any fertile couple.
For many years, the terms PGS and PGD were used. And PGS was usually meant to be the test that you are doing on the embryo when the parents do not really have a higher genetic risk, and you just want to confirm whether they are genetically normal or not. PGD was usually used when the patients had some kind of abnormalities, but this terminology is no longer used.
We now refer to it as a PGT-A when you want to check if there are any aneuploidies, so that means numerical abnormalities of the chromosomes. PGT-SR when you are trying to discard translocations of the chromosomes. PGT-M when you are trying to discard mutations inside the chromosomes. Mutations that the patients are known-healthy carriers and that can cause problems in the babies.
PGT-A, PGT-M, PGT-SR, those complicated terms are for the genetic testing of the embryo. It should be done if you have any genetic problems in your family, and you are aware of it, or if you are in advanced age 45-50 plus, and you want to be sure that your baby is genetically healthy.
PGT-A mean pre-implantation genetic testing for aneuploidy, which means changes in the number of chromosomes. The most common one is chromosome 21, which is Down Syndrome, chromosome 18, and 13.
The next one is PGT-M, which stands for monogenic diseases. Those are single-gene mutations such as cystic fibrosis and other diseases that we can check, or you know for sure that the disease is in your family. The third one is PGT-SR, pre-implantation genetic testing for structural arrangements, which means that there is no change in the number of chromosomes, but there are chromosomal translocations or inversions.
Your doctor will recommend which one of those you need in your situation. Make sure that you talk about it with your parents, grandparents, etc., to find out whether they had any congenital genetic problems in the family.
