Preimplantation genetic diagnosis (PGD) is primarily performed to diagnose single gene defects in embryos from couples known to be carriers of a genetic disease. It can be used to test for autosomal recessive diseases (e.g. cystic fibrosis), autosomal dominant diseases (e.g. Huntington disease), X-linked diseases (e.g. Fragile X syndrome) and others such as Rh factor incompatibility. PGD requires the construction of DNA probes or materials specific to the genetic profiles of the parents and possibly grandparents which can take weeks to months prior to commencing treatment. Accordingly, fees for PGD are generally higher than for PGS.
Both PGS and PGD require the biopsy of a small number of cells from each embryo 5 to 6 days after fertilization at the blastocyst stage of development. At this stage cells can be taken from what will become the placenta, avoiding the portion of the embryo that will form the fetus. The cells are sent to a genetic testing lab while the embryo is cryopreserved and remains in storage at the RMSCVA Laboratory. Once the genetic results are obtained, appropriate embryos can be thawed and transferred into the uterus of the patient or a gestational carrier.