How does PGD work?
PGD is performed as part of the IVF process. For all couples the following steps will be performed:
- Female partner takes medications to stimulate the ovaries to make multiple eggs grow
- Eggs are retrieved with a transvaginal needle in an office procedure
- Eggs are fertilized by sperm using a process called ICSI
- Embryos develop in the embryology laboratory over the course of 5-6 days
On day 5 or 6 of development, when embryos have reached the blastocyst stage, a few cells that would eventually become placental cells are removed from the outer layer of the embryo (this is called a trophectoderm biopsy). The cells are then sent to a special laboratory that will test for the specific abnormality in question using the most advanced techniques.
The embryos are frozen immediately, using vitrification. When the results are returned, normal embryos can be thawed and placed back in the uterus in a subsequent frozen embryo cycle.
Of the embryo(s) that are not affected by the genetic disorder or chromosomal abnormality, the best quality embryo(s) are selected for transfer to the uterus. If additional unaffected and good-quality embryos are available, they may remain cryopreserved for a future embryo transfer.
Can PGS be performed at the same time as PGD?
Yes. Embryos can be screened for chromosomal abnormalities that occur as a result of aging in addition to heritable genetic diseases or specific heritable chromosomal disorders.
At what stage is the embryo biopsied?
Historically, embryos were biopsied on day 3 of their development when the embryo only contains 6-8 cells. Recent literature suggests that when then embryo is allowed to develop to the blastocyst stage at day 5 or later when the embryo has 200 or more cells, then the biopsy is safer. With day 5 biopsies, the cells are removed from the outer layer of embryo which will eventually become the placenta, without harming the cells that will eventually become the baby.
Do I still need to have genetic testing during the pregnancy?
No, preimplantation genetic diagnosis does not replace prenatal testing, such as cell-free fetal DNA testing, chorionic villus sampling (CVS) or amniocentesis. Though preimplantation genetic diagnosis is thought to be highly accurate, testing should be repeated during pregnancy. In addition depending on the extent of testing that is done at this stage, additional testing for other chromosomal abnormalities may also be warranted during pregnancy. Therefore, prenatal testing is still recommended and currently remains the standard of care.
Is PGD safe?
Thousands of clinical preimplantation genetic diagnosis cycles have been performed worldwide, resulting in the birth of hundreds of healthy babies. PGD was introduced in 1990 and has been increasing used since that time. The procedure does not appear to affect the development of the embryo and subsequent pregnancy or the child once it is born. However, more follow up studies of children born after PGD are needed.