You can look at PGT as a very early prenatal diagnosis. If you run the risk of passing on a hereditary condition to your child(ren), you can also find out via an invasive prenatal test (chorionic villus test, amniocentesis, umbilical cord puncture) whether the foetus has inherited the condition. We call this ‘invasive’ testing because we remove material (tissue or fluid) from the foetus, the womb or the placenta.
In PGT the diagnosis is not made during the pregnancy but in the embryos created in vitro, before one (or more) of them is (are) replaced in the womb. In other words you are given the opportunity to become pregnant without the future baby inheriting the genetic condition. Therefore you can avoid the difficult decision of having to terminate the pregnancy or not.
- PGT can be carried out to detect an abnormality in the chromosomes (number, structure) or in one gene (in the case of monogenic disorders). The aim being to work out which embryos are affected and which are not: only the latter are returned to the womb.
- In an X-linked condition (in which boys run a high risk of inheriting the disease) in certain cases the test must be carried out to determine the sex of the embryos. Therefore the possible birth of a boy with the disease can be prevented.
- Furthermore there is a special test used to determine the tissue type of the embryos which is also called HLA typing. The aim of this is to detect which embryos have the same tissue type as an already ill child of the same parents. Children with a certain (fatal) blood or immune disease, for example, can sometimes be cured by the transplantation of blood stem cells or bone marrow cells.
That is only possible if the transplanted cells are HLA-compatible with the cells of the sick child, if not they should be discarded. A baby born after medically-assisted reproduction treatment with HLA typing via PGT can, in other words, be a donor to save a sick brother or sister. Therefore a baby of this kind is also referred to in the media as a ‘saviour baby’ or donor baby’.