Preimplantation Genetic Diagnosis (PGD)
- The patient’s embryos can be tested for genetic abnormalities before they are transferred to the uterus. This is called preimplantation genetic diagnosis, or shortly PGD. It is a diagnostic procedure, which is an optional step in IVF. PGD makes it possible for couples or people who have or who carry serious inherited disorders to decrease the risk of passing the disorder to their children. This is a new hope of having a healthy child.
However, no single test can accurately predict the risk of all defects in a child. Many birth defects, such as those related to environmental and toxic exposures and those that are random and unexplained, have no genetic background. Therefore, it’s often hard to detect it with genetic testing.
PGD is similar to a classic IVF technique with an optional procedure in a cycle. A woman takes medication to stimulate ovarian function. In a few days, the eggs are removed from her body and then fertilized by sperm in a laboratory dish. Once, the embryo becomes mature, one or more cells from an embryo are sent for a genetic testing. This will show if an embryo is normal (no disease) or affected (has the disease). At the same time embryo is growing in the IVF laboratory. Genetically healthy embryos are transferred to the uterus.
Preimplantation genetic testing (PGT) includes preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS). These terms are frequently used interchangeably. PGD is an option to find a specific, known genetic disorder. For example, if one of the parents carries a gene of the systemic disease called Cystic fibrosis or suffers from this disease. PGS involves testing an embryo for chromosomal abnormalities. Patients with recurrent pregnancy loss, severe male factor infertility, recurrent IVF treatment failures or in advanced reproductive age should consider PGS. Therefore, a patient should consult with a doctor to choose a right test.
PGT is used in the following cases:
- To identify single gene diseases. The most frequently diagnosed diseases are Cystic Fibrosis, Tay-Sachs, Sickle Cell Disease, Thalassemia, Spinal Muscular Atrophy
- To prevent sex-linked disorders, such as Duchenne muscular dystrophy and Fragile X syndrome. Parents can choose a sex, if there is a risk for a particular disease that is much more prevalent in boys or girls.
- To understand the reasons of medical conditions as recurrent pregnancy loss, implantation error, severe male factor infertility, advanced reproductive age or recurrent IVF treatment failure.
- Families in search of a bone marrow donor may be able to use PGT to bring a child into the world that can provide matching stem cells for an affected sibling.
- To evaluate cancer predisposition.
Some couples also can choose to do PGS for personal reasons, religious view and for balanced family planning.
Anyone considering PGD should consult with a fertility specialist or a reproductive endocrinologist. Not all disorders can be detected with PGD. Besides, PGD is currently offered only in a few centers and may offer under the supervision of an institutional ethics review board.