Preimplantation genetic diagnosis (PGD) is a method to assess the genetic health of embryos created in an IVF cycle. After eggs are fertilized with sperm and develop into embryos with at least eight cells, one of the cells from each embryo is removed under a microscope, and the chromosomes of that cell is analyzed to determine whether the embryo is genetically normal or not.
There are a number of genetic diseases and chromosomal abnormalities that can be detected by PGD. Thus, PGD benefits patients who are carriers of genetic diseases and prevent the diseases from being expressed in their children and parents who want to avoid having chromosomal abnormalities in children. A common example of chromosomal abnormalities that can be detected by PGD is Down's syndrome. In a more complicated process, PGD can pick up inherited genetic diseases like Tay-Sachs disease, Cystic Fibrosis, Sickle Cell disease, Huntington's Chorea disease, Cooley's Anemia, and many others.
PGD is also used in gender selection processes, where parents who want to have a child of a specific gender have only embryos of the desired gender transferred to the uterus. While gender selection methods based on sorting of sperm (between those with X chromosome and those with Y) has a lower success rate, gender selection with PGD is nearly 100% accurate.
At the Center for Human Reproduction, all embryos remain onsite and are never shipped out, ensuring maximum safety and reducing the risk of mix-ups. Preimplantation genetic diagnosis became widely available in the 1990s, but it wasn't until 2001 that the American Society for Reproductive Medicine (ASRM) and the Society for Assisted Reproductive Technologies (SART) declared the procedure no longer experimental. However, despite its advancements, PGD carries certain risks, including the possibility of false positive or false negative diagnoses due to mosaicism, where not all cells in an early-stage embryo are identical. A biopsy of a cell with an abnormal chromosome that isn't present in other cells could lead to inaccurate results.
Embryos can naturally isolate and remove genetically abnormal cells, meaning that embryos flagged as abnormal during PGD may correct themselves and develop into healthy babies. Despite this, long-term outcomes for offspring born after PGD have not been thoroughly established. There is also a small risk that removing a cell during the biopsy could damage the embryo, potentially leading to lower pregnancy chances compared to embryos that have not undergone PGD.
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