Patients facing known genetic risks for having a healthy baby now have treatment options through in vitro fertilization. Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) are laboratory procedures performed at RMSCVA that, when coupled with IVF, can provide information about the genetic health of an embryo prior to placement in the patient’s uterus in an attempt to establish pregnancy.
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.
PGS is performed to screen for embryonic abnormalities in chromosome number (aneuploidy) or structure (translocation) which commonly lead to implantation failure, pregnancy loss or birth defects. As women age, the incidence of these aneuploidies increases and is a primary reason for age-related decline in fertility. By using PGS, couples can identify those embryos with the correct number of chromosomes, greatly increasing their chance of success.
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.