PGD & PGS

Preimplantation genetic diagnosis (PGD)

PGD is a genetic diagnosis technique that provides information about the gene structure of cells in an embryo.

An embryonic biopsy is used – about 3 to 8 cells from a 5-day embryo (blastocyst stage). The harvested cells are sent to the laboratory for testing. After the biopsy, the embryo is frozen and preserved until transfer and implantation.

The PGD is able to identify approximately 2,000 genetic diseases, it has 98% accuracy and it is used to identify healthy embryos. It is generally useful to couples with a family history of genetic diseases that can be inherited by their children.

Specific markers of certain diseases, such as monogenic disorders, including cystic fibrosis and sickle cell disease, X chromosomal fragility, and Duchenne muscular dystrophy, can be identified by using the preimplantation genetic diagnosis technique.

Preimplantation genetic screening (PGS)

PGS is used to determine whether the cells in an embryo have the normal number of chromosomes (46).

A biopsy from a 5-day embryo (blastocyst stage) is used. The embryonic cells are then sent to a laboratory that uses the technique to identify the number of chromosomes in each cell. Embryos with a normal number of chromosomes are called „euploid” and those with an abnormal number are called „aneuploid”. The aim of PGS is to prevent the transfer of an abnormal embryo to the uterus.

As all women/men will have some eggs/sperm that are chromosomally abnormal, all couples are at risk of having abnormal embryos. This risk significantly increases as a woman gets older.

An abnormal embryo almost always fails to implant or, if it does, it ends with a biochemical pregnancy (hormonal evidence of pregnancy only), miscarriage, foetal death later during pregnancy, or birth of a child with severe health problems.

Couples undergoing IVF (in vitro fertilization) can make use of PGS if they:

have been diagnosed with severe male infertility,
had recurrent IVF failures,
had multiple miscarriages,
age over 35 years.

Pre- and post-test genetic counseling

Pre-test genetic counseling has to inform the individual:

What is the test for?

symptoms, natural history of the disease,
prospects of prevention, or treatment,
inheritance pattern, the risk of the disease in the counselee’s situation,
reliability and limitation of the test
possible psychological impact and other consequences of the test result.

Possible uncertainties due to the present lack of knowledge should be declared.
The counselor should offer assistance in the decision making

A written summary of the discussion should be prepared.

Post-test genetic counseling should give information about:

Whether the test has to be repeated because of possible uncertainties.
A follow-up plan should be discussed.
Depending on the disease being tested a consultation with a psychologist or follow-up contact with the genetic counseling unit should be offered.
A written summary of the test result should be given to the counselee.
Written material to help the counselee to spread the information in the family may be offered.