Preimplantation genetic Testing (PGT) includes both terms PGT (S) – screening for chromosome numbers and PGT (D) – screening for diagnosis of inherited disease. Cells taken from an embryo are tested for genetic diseases and/or chromosomal disorders. Cells are removed from the embryo on day 3 or day 5 of development and sent for chromosomal analysis. Day 5 or blastocyst biopsy gives better results.
The goal of PGT(S) is to identify normal embryos for transfer to improve pregnancy rate and reduce risk of abortion. Thus it is helpful in women with repeated IVF failures and repeated pregnancy loss.
PGT (D) can identify the presence of chromosomal translocations present in a partner (rearrangements of parts of chromosomes). Such translocations may be responsible for repeated pregnancy loss. PGD is also used to detect single gene disorders (genetic diseases that are a result of a single mutated gene). There are over 4000 single gene disorders. The most common diseases tested for are Cystic fibrosis, Tay Sachs, Fragile X, Myotonic dystrophy and Thalassemia. These disorders can be passed on to the offspring.