Amniocentesis and chorionic biopsy are reliable but invasive methods that are only possible between 10 and 15 weeks of pregnancy. In the case of a diagnosis of a genetic disease in the fetus, it is necessary to decide on a possible early artificial termination of pregnancy. 

The procedure is intended for the following couples: 

• carriers of chromosomal abnormalities
• carriers of sex-linked hereditary diseases
• carriers of genetic mutations 
• frequent unsuccessful in vitro fertilization (IVF) procedures and spontaneous abortions. 

An irregular number of chromosomes (aneuploidy) often occurs in older women (over 37 years) as a result of incorrect separation of chromosomes during the formation of gametes. The most common examples are Down’s syndrome and Klinefelter’s syndrome (47, XXY), which is a common cause of azoospermia in men.

In the PGD procedure, the couple must go through a routine IVF procedure, which allows the embryo to be fertilized and grown outside the mother’s body, regardless of the couple’s fertility. After the diagnosis, only embryos that are reliably healthy can be returned to the uterus. 

• The first part of the PGD procedure consists of the ICSI method, which prevents the accidental isolation and testing of the egg cells or the sperm, which are present in the medium with the embryo, if the classic IVF technique would be used. Fertilized egg cells (zygotes) are grown in an incubator until the 3rd day, when it is the most suitable time to collect the cells of the developing embryo. A viable embryo at this stage has 6-8 cells or blastomeres. With the help of an acid or a laser, part of the envelope that protects the dividing cells of the embryo during the first days is removed, which makes it possible to remove one or two blastomeres with a thin biopsy pipette. The biggest obstacle to implementation is the insufficient number of suitable embryos.
• The second part of the PGD procedure is the isolation of genetic material from the nucleus of the removed cell and molecular biological investigation (fluorescent in situ hybridization – FISH or polymerase chain reaction – PCR). 
• The embryos are stored while genetic material inside the removed cells is tested for abnormalities. One of Genetic & IVF’s genetic counselors discusses PGD test results with the woman/couple, and a frozen embryo transfer (FET) cycle is planned for use of the embryo(s). Decisions regarding selection of embryos to transfer into the uterus are made with the advice of both the medical and genetics team.
• Embryos that have both a normal test result and appearance (morphology) can be transferred in a frozen embryo transfer (FET) cycle. While embryo morphology can be helpful in selecting the best embryos for transfer, it is known that many embryos with significant chromosome abnormalities have normal morphology. Therefore, PGD results help to better identify the best embryos to transfer to the uterus to achieve a successful pregnancy. The combination of normal genetic testing with normal physical appearance indicates the highest chance of becoming a healthy pregnancy. All decisions regarding which embryo(s) to transfer to the uterus and how to use the remaining embryos are made together between the couple and their medical team.

With every PGD procedure, there is also the possibility of a wrong diagnosis, as the diagnosis must be made on one or two cells, which is a challenging task even for extremely experienced genetician.