AN OVERVIEW OF PREIMPLANTATION GENETIC DIAGNOSIS (PGD) TESTING

Preimplantation genetic diagnosis (PGD) is a laboratory procedure, used in conjunction with in vitro fertilization (IVF), to reduce the risk of passing on genetic disorders. Some of the most common reasons for PGD is testing embryos for specific disease (such as cystic fibrosis or sickle cell anemia) or testing for chromosomal abnormalities that a parent carries. Families may also use PGD when a member of the family needs a bone marrow donor, as a way to have a child who can provide matching stem cells.

More recently the most common reason for PGD is testing for “aneuploidy diagnosis” , which is testing the embryos for chromosomal abnormalities in women who have had recurrent miscarriages or at high risk for having a baby with a chromosomal defect (such as Down’s syndrome) due to age. Embryos with an abnormal number of chromosomes, a condition called aneuploidy, usually fail to implant, making this an important success factor in IVF.

During the IVF cycle, aneuploidy screening will help to determine which embryos contain a full set of chromosomes, and which ones contain an abnormal number of chromosomes, it is theorized that doing PGD on all women over 35 will significantly increase their chance of success and decrease the chance couples will have a baby with a chromosomal abnormality.

Testing for single gene defects– Typically, couples in need of PGD for a specific disease are not infertile but have a family history of a condition and want to reduce the risk of having  a child or another child with significant health issues or early death. PGD is available for almost any inherited condition for which the exact genetic mutation is known. A unique test must be developed for each couple undergoing IVF with PGD for single gene disorders, and the test may take up to several months to design before beginning the IVF with PGD cycle.

Testing for chromosomal abnormalities– All women have some risk of having a baby with chromosomal abnormalities, a risk that dramatically increases with age. PGD is a technique used to test the embryos, for chromosomal abnormalities prior to implanting them in the uterus. Using PGD in women of advanced age undergoing IVF will decrease the chance that a woman of advanced age will have a child with a chromosomal abnormality.  Additionally, PGD for chromosomes can be used in women with multiple miscarriages.   The most common cause of miscarriage is the baby has a chromosomal abnormality. Patients who have experienced multiple miscarriages in the past may consider a PGD screening to avoid future pregnancy losses due to genetic problems.

When are the embryos tested? Currently, a typical preimplantation genetic diagnosis biopsy is can be performed on the embryo at day 3 or 5  of development. On day 3, the embryo is tiny—composed of only six to eight cells—and only one cell is removed for genetic diagnosis, One day 5 (or 6) the embryo contains many more cells (over 100) and the biopsy can remove several cells from the embryo making the results more accurate.

Additional research has also shown that abnormalities seen at day 3 can actually correct themselves by day 5. Performing the PGD on day 5 has led to significant improvements in implantation rates and excellent results for patients. However,  with Day 5 biopsy often the embryos need cryopreserved and transferred at a later date.

Should we consider PGD?

For couples undergoing IVF, preimplantation genetic diagnosis may be recommended when:

• One or both partners has a history of heritable genetic disorders (testing for single gene defects)
• One or both partners is a carrier of a chromosomal abnormality
• The mother is of advanced maternal age
• The mother has a history of recurrent miscarriages

Rocky Mountain Fertility Center is one of the top fertility clinics in the midwest, with a Board Certified Colorado reproductive endocrinologist offering fertility options with high success rates. Dr. Oscar Perez is the Director of the Embryology and Andrology Laboratory. Dr. Perez is an expert in all the laboratory components of embryology and andrology related to assisted reproduction, including, but not limited to IVF, ICSI, PGD, and cryopreservation. His PGD expertise is impressive, and his expertise is considerable when it comes to assisting patients achieving their fertility goals.