Preimplantation genetic screening (PGS) is a type of genetic screening test based on the determination of the correct number of chromosomes of the cells in an embryo. Chromosomal abnormalities are responsible for the failure of the implantation of the embryo into the uterine cavity and of miscarriage.
Although PGS is not a test for a specific genetic disorder, the Down syndrome – also known as trisomy 21 which is characterized by the presence of an extra chromosome 21 – can be detected by PGS.
Preimplantation genetic diagnosis (PGD) is another genetic screening test used to detect the presence of mutated genes for specific genetic disorders or diseases, such as Huntigton disease, Marfan syndrome, Cystic fibrosis, Tay-Sachs disease, X chromosome related genetic diseases (Hemophilia, Duchene muscular dystrophy), abnormalities in the number of chromosomes.
This test is crucial to prevent passing genetic disease or disorders on to a child, if there is a family history in one or both of the couples.