What is Preimplantion Genetic Diagnosis?
Preimplantation genetic diagnosis (PGD) is a reproductive technology used along with an IVF cycle to increase the potential for a successful pregnancy and delivery. PGD is a genetic test on cells removed from embryos, to help select the best embryo(s) to achieve pregnancy or to avoid a genetic disease for which a couple is at risk.
Who should consider PGD?
PGD may be considered in all IVF cycles; however, those who might benefit most from this test are couples at increased risk for chromosome abnormalities or specific genetic disorders. This includes women who have had several miscarriages, or who have had a prior pregnancy with a chromosome abnormality. Women over 38 years of age and men with some types of sperm abnormalities may produce embryos with higher rates of chromosome abnormalities. This test is also known as PGT-A (aneuploidy). In addition, if a person carries a structural rearrangement of the chromosomes, PGD can identify which embryos have a normal amount of chromosomal material. This technology is also known as PGT-SR (structural rearrangement). When there is a 25% or 50% chance to have a child affected with a specific genetic disease, PGD can be designed to identify which embryos are affected, unaffected, or a carrier (if applicable) for that disease. Then, only embryos without the disease are transferred to the uterus to attempt pregnancy. This is also known as PGT-M (monogenic disorders).
What are the PGD steps during an IVF cycle?
After embryos are created in the laboratory, they are grown for five to six days. On day five or on day six, the biopsy for PGD is done on all appropriately developing embryos. Biopsy involves removing a few cells from the trophectoderm, or the layer of cells that is ‘hatching out’ of the embryo at this stage of development. The embryos are stored while genetic material inside the removed cells is tested for abnormalities. One of Genetic & IVF’s genetic counselors discusses PGD test results with the woman/couple, and a frozen embryo transfer (FET) cycle is planned for use of the embryo(s). Decisions regarding selection of embryos to transfer into the uterus are made with the advice of both the medical and genetics team.
Is embryo biopsy and PGD safe?
Yes. Data from many years of PGD in animals and several hundred thousand live births in humans indicate that PGD does not lead to an increase in birth defects over that of the general population. Follow-up evaluation of children born after PGD does not show any evidence for a detrimental effect of the process on growth or neurological development over the first several years of life. In embryos where chromosomal PGD testing is performed, one can expect fewer pregnancies ending in miscarriages due to chromosomal disorders since most abnormalities are identified prior to transfer of the embryos to the uterus. Removal of a few of the trophectoderm cells of the early embryo does not alter the ability of that embryo to develop into a complete, normal pregnancy.
How are embryos chosen for transfer?
Embryos that have both a normal test result and appearance (morphology) can be transferred in a frozen embryo transfer (FET) cycle. While embryo morphology can be helpful in selecting the best embryos for transfer, it is known that many embryos with significant chromosome abnormalities have normal morphology. Therefore, PGD results help to better identify the best embryos to transfer to the uterus to achieve a successful pregnancy. The combination of normal genetic testing with normal physical appearance indicates the highest chance of becoming a healthy pregnancy. All decisions regarding which embryo(s) to transfer to the uterus and how to use the remaining embryos are made together between the couple and their medical team.
Where does the PGD testing occur?
PGD is performed at Genetics & IVF Institute’s onsite PGD laboratory.( The laboratory has been performing testing on embryos since 1993, and since then the PGD staff has performed more than 3000 PGD cycles. Because the PGD laboratory is onsite, shipping and coordination with a separate laboratory elsewhere is not necessary. Patients need not worry about their embryo biopsies being sent to an off-site lab to be tested. Rather, everything takes place at our fertility center in Fairfax, Virginia allowing improved coordination between the Embryology and PGD laboratories as well as the clinical staff.