What is preimplantation genetic diagnosis (PGD)

fertile eggIf you are considering fertility treatments involving in vitro fertilisation (IVF), the topic of preimplantation genetic diagnosis will inevitably come up. So, what does this mean?

Preimplantation genetic diagnosis, or PGD, is a screening test used to check embryos for inherited diseases. The test screens for genetic or chromosomal disorders that may be present in the embryos and helps couples make more informed decisions regarding the next steps in the IVF process. In other words, PGD allows couples to select unaffected, healthy embryos that will have the best chance of developing into a full-term baby.

Though PGD is not used in every single case of IVF, it is usually recommended in the following scenarios:

  • The mother is of advanced age – typically 40 and older
  • There is a history of recurrent miscarriage
  • One or both parents have a history of heritable genetic disorders or chromosomal abnormality

embryoCurrently, PGD is approved to screen for more than 250 genetic conditions, but it can be used to test for virtually any genetic condition in which a specific gene is known to cause that condition. If you want to screen for a condition that is not already approved, your fertility clinic will need to apply for a special licence to carry out that testing.

If you are planning to have PGD, the embryo biopsy will be performed after you undergo the normal IVF treatment to collect and fertilise the eggs. After three days of culture in the laboratory, the embryos are ready for the test. This is because by the third day, the embryos will typically be 8-cell embryos and the test involves the removal of one of two cells. Once the results are in, the best quality embryos are selected for transfer to the uterus after two more days in the lab.

In other cases, the biopsy can be done on day five or six, when the embryo consists of many more cells and is known as a blastocyst. After the test results are in, the good blastocysts will be frozen for later transfer into the uterus.

It is important to know that PGD does not replace prenatal testing such as the amniocentesis or chorionic villus sampling. PGD simply provides diagnostic information based on the review of a single cell. This means prenatal testing is still a required part of the pregnancy, should one result. It is also important to know that with PGD, there are some risks, though relatively low. The process of the cell removal may damage some embryos and the test results are not always 100% conclusive.

You may also be wondering if having the PGD test means the chance of having a baby is increased. Remember, PGD is a diagnostic test, and is intended to help couples avoid having a child with a genetic disease. The success of fertility treatments and IVF depend on many factors including the parents’ age, cause of infertility, and the quality of the eggs and sperm.