What is Preimplantation Genetic Diagnosis (PGD) and Preimplantation Genetic Screening (PGS)?
Preimplantation Genetic Diagnosis (PGD) is a method used to evaluate genetic conditions within embryos prior to them being placed into the uterus for pregnancy. When certain genetic conditions are known to be carried in the parents and there is a risk of transmission to the offspring, then PGD may be used to avoid passing the mutations on. It is a state of the art procedure used in conjunction with in-vitro fertilization to help select embryos free of known genetic conditions for transfer into the uterus and improve the outcomes for the offspring.
Preimplantation Genetic Screening (PGS) is a method used to screen the chromosomes of an embryo. As the ovaries age, the eggs produced are at greater risk for chromosome abnormalities. Chromosomes are large segments of genes and critical to normal development. If an egg contains an extra chromosome or is missing a chromosome then this abnormality will be transmitted to the embryo. Most of the chromosome abnormalities are incompatible with normal development and life. PGS evaluates the chromosomes of the embryo to confirm that there are a normal number present, giving the embryo an optimal chance to result in a healthy baby.
When Is PGD Recommended?
Indications for PGD include recurrent miscarriages related to translocations and inherited genetic disorders such as Cystic Fibrosis and Muscular Dystrophies.
When Is PGS Indicated?
Preimplantation genetic screening is useful in patients who are at risk for chromosome abnormalities. Woman of advanced reproductive age and those with recurrent miscarriages are at particularly high risk and PGS is recommended
How Does PGS / PGD Work?
For patients who are at high risk of having offspring with chromosomal or genetic abnormalities, they may elect to undergo PGD/PGS. PGD/PGS can only be performed as part of an invitro fertilization (IVF) cycle.
When embryos are created during IVF and reach a particular stage of development, they can be biopsied. The biopsy consists of the removal of 4-6 cells from the embryo so that they may tested.
The embryo is frozen and stored while the cells are being tested. Typically, two weeks later, the results are available, and the unaffected embryos are then selected to be transferred back to the uterus.
What Types Of Genetic Or Chromosomal Testing Can Be Done On Embryos?
There are currently several hundred single genes that can be tested depending on the gene of interest. Examples of such genetic mutations include cystic fibrosis and muscular dystrophy.
In a normal embryo, there are 23 pairs of chromosomes, either 46XX or 46XY. As women age, the risk of having chromosomal abnormalities in the embryo increases. One of the most common abnormalities is Down’s syndrome, a condition having 47 chromosomes including an extra chromosome 21.
The current technology allows us to evaluate an embryo and confirm that there is a normal number of chromosomes prior to placing it back into the uterus. Miscarriage rates are thereby lowered due to the transferring of genetically normal embryos.
Is There An Additional Charge For PGD/PGS?
Although the biopsy is performed at our center, the testing of the single cell is performed elsewhere at a special laboratory. The outside laboratory does charge an additional fee for their services and this fee varies depending on the type of testing being performed.
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