Preimplantation genetic diagnosis (PGD) is also called Preimplantation Genetic Testing (PGT). It is a procedure used before implantation to find genetic changes within embryos genes or chromosomes. The embryos are created by using the technique called in vitro fertilization. The goal of PGD is to prevent certain diseases or genetic changes from being passed on to the child. The genetic change must be known before this procedure can be done.