Pre-Implantation Genetic Diagnosis
What is pre-implantation genetic diagnosis (PGD)?
PGD is a method of testing embryos produced during a treatment cycle. They are tested for particular genetic disorders before they are transferred to the uterus.
Who is pre-implantation genetic diagnosis for?
PGD is used for patients at high risk of transmitting a specific inherited disorder to their children.
How does PGD work?
As long as a genetic disease has an identified mutation, PGD should be possible. You will need appropriate genetic counseling and to check that the HFEA licenses the testing of this condition. An HFEA license has to be in place for each condition. It may be necessary to apply for a license for your particular condition and this process can take up to 16 weeks.
The preparation for PGD involves the design of a specific custom-made probe for a couple that will look for the single gene in embryos produced during a treatment cycle. This may require testing of blood or buccal cells from the couple and potentially other affected family members. The time required for preliminary testing is extremely variable and may take a number of weeks depending on the disorder.
The ovaries are stimulated and eggs are collected and then fertilised using intracytoplasmic sperm injection (ICSI). The use of ICSI reduces the risk of DNA contamination derived from sperm. A single cell can be removed for testing three days after fertilisation. Alternatively, 5-10 cells can be taken on day-5 (blastocyst stage). The embryos under analysis do not leave the IVF clinic. They are either returned to the incubator or cryopreserved until test results are available.
The cells are analysed independently using the developed probes and the results available within 24-36 hours. Appropriate embryos for transfer can then be chosen based on these genetic results.
What are the risks of PGD?
No screening test is 100% accurate, so following any genetic screening it is recommended that patients who become pregnant undergo prenatal testing which will reveal whether the genetic diagnosis was correct, and confirm whether or not the fetus is unaffected by the specific disease or mutation.