Pre-implantation Genetic Diagnosis and Screening (PGD/PGS)
PGD and PGS are terms used to describe testing an embryo for a specific genetic disease which it could inherit from the parents.
PGD is usually the diagnosis of a single genetic defect in an embryo for couples that have only one genetic mutation and want to ensure it is not passed on to their baby. Typically, these groups have a 25-50% risk of transmitting the disease to their child.
PGS usually refers to the screening of chromosomes for aneuploidy (abnormal number of chromosomes). PGS is a term often used by doctors treating infertility, and especially in cases of advanced age, several failed in vitro fertilizations, or those cases with children with chromosomal anomalies in their past (regardless of how the previous pregnancy was achieved).
Some of the genetic diseases that can be treated through PGD include:
- Cystic Fibrosis
- Hemophilia
- Huntington’s Disease
- Marfan’s Disease
- Muscular Dystrophy
- Thalassemia
- Tay Sachs
- Spinal Muscular Atrophy
- Sickle Cell Anemia
PGS identifies embryos containing chromosomal anomalies which could result in a failed in vitro fertilization, repeated miscarriages, children born with Down syndrome, or other aneuploidy syndromes.
Both, PGD and PGS imply the testing of embryos through the analysis of their cells. Both require In Vitro Fertilization! In this way, we have the opportunity to catch genetic anomalies in embryos before transferring them to the uterus and thus select the normal embryos (those without anomalies) for transfer.
PGS and PGD can be done on day 3 or day 5 of the embryo's life. Usually, a cell is isolated from the embryo (effectively, we have an embryo biopsy). This cell is analyzed for genetic or chromosomal anomalies. The analyzed cell has the same genetic content as the embryo cells from which it was taken. This type of biopsy does not harm the embryo being analyzed since the remaining cells have the same composition and the same developmental potential.
After the biopsy and the analysis of the embryonic genetic material, embryos can be selected based on the absence of anomalies.
The advantages of PGD / PGS include high chances of pregnancy in In Vitro Fertilization, reduction of the chances for multiple pregnancies, reduction of the chances of miscarriage or for the birth of the aforementioned anomalies.