Preimplantation genetic diagnosis (PGD) involves the testing of embryos for genetic abnormalities, usually in conjunction with in vitro fertilization (IVF), which is the process of mixing egg cells with sperm in a dish. With IVF, once the eggs are fertilized, they are placed into the woman’s uterus to enable pregnancy, rather than the traditional method of having the eggs fertilized inside the womb.
Preimplantation genetic diagnosis is normally done when there is a history of genetic diseases in the family or if either of the parents have a genetic abnormality. It is also performed when women wish to become pregnant later in time, after the age of 37. Women who have experienced several miscarriages may consider this option, as well as women who failed to conceive with frequent attempts of in vitro fertilization.
The Stimulation of the Ovaries
Fertility medications are used to stimulate the ovaries in order to create multiple eggs. These are normally administered by injection. There are some side effects that can occur such as an allergic reaction, infection, bruising or swelling at the site of injection, hematoma (blood clot) and hyperstimulation of the ovaries (excessive stimulation of the ovaries).
How Preimplantation Genetic Diagnosis Is Performed
Although Preimplantation Genetic Diagnosis is very successful at predicting genetic disorders and diseases before a child is born, it cannot guarantee a healthy child. The process can be very complex, and medical studies have shown that results may not always be correct.
The Embryo Biopsy
On the 3rd day of in vitro fertilization, an embryo biopsy is performed by using micromanipulators (a device that is used to manipulate needles and instruments to perform delicate procedures). The embryo remains in place with the help of a pipette (glass or transparent plastic tube). A glass needle then punctures a hole in the shell of the external layer of the embryo (zona pellucida) or with the use of a laser.
A single blastomeric (single cell) is retrieved from an 8-cell embryo by using gentle suction. This sample can then be sent to the laboratory for genetic testing.
Techniques Used for Genetic Testing
Two different techniques are used to test the embryo for genetic abnormalities. The PCR (polymerase chain reaction) technique for single-cell diagnosis allows for multiplication (DNA) for testing. Up to nine chromosomes may be tested. After the process is done, the embryos are kept in a growth media to allow for further division. Once the diagnosis is complete, the other embryos may be transferred again into the uterus for the in vitro fertilization treatment.
With the FISH (fluorescent in situ hybridisation) technique, specially chosen fluorescent flexible devices (probes) are used to test the chromosomes for the testing of genetic diseases. Glowing molecules (fluorochromes) can attach to certain chromosomes, and up to 10 may be tested at one time.
Duration of Process
The treatment cycle itself normally takes about 8 to 9 weeks, but because of the necessary preparation and pre-testing, there is the possibility of one year before the preimplantation genetic diagnosis process can begin.