Pre-implantation genetic diagnosis (PGD) refers to removing a single cell from a Day 3 embryo and assessing this for any chromosome or genetic abnormalities that may be present within the embryo.
Why use PGD?
A surprisingly large number of embryos will have a chromosome abnormality present. The rate at which this happens rises with the increasing age of the woman. Studies have proven that at the age of 40, up to 50% of embryos can be abnormal. These chromosomally abnormal embryos may fail to grow in the IVF culture and, therefore, are not considered for embryo transfer. Often the abnormal embryos can appear quite normal under the microscope and by laboratory standards.
The aim of PGD is to select chromosomally normal embryos for transfer, so that the chances of pregnancy with the outcome of a healthy baby are maximized. For couples with a known genetic problem, for example, both the male and female patients are carriers for cystic fibrosis. PGD testing can be available to prevent a pregnancy with an affected child.
How PGD Works
At Fertility Solutions, when an embryo reaches the 6 to 8 cell stage, a hole is made in the outer shell around the embryo (the zona). One, or maybe 2 of the cells in the embryo are taken out for PGD testing.
The cell that is processed for testing is examined to check that it has the correct number of chromosomes present. Abnormal numbers of chromosomes can be associated with Down’s syndrome and Turners syndrome.
It is not possible to check for every known genetic disease. There are, however, a number of tests for known specific genetic diseases available that can be done on a single cell. When the results have been reported to the Fertility Solutions scientist, the embryo/s is either transferred into the uterus, frozen for future use, or discarded if the results are abnormal.
What Are The Possible Problems With PGD?
- Mosaicism. This condition is where there is a chromosome defect in only some of the cells within the embryo. This means that some of the cells within the same embryo are normal. In this situation, it can be possible to have a normal chromosome result from an abnormal embryo. If this embryo is returned to the uterus, then the birth of an abnormal baby can result.
- Embryo Damage. The process of removing the cell for testing can damage the embryo and it can fail to develop any further, or might not implant to go on to a pregnancy.
- Genetic Conditions. PGD for genetic conditions like Cystic fibrosis, is only useful when you know what you are looking for and you know what genetic abnormality both parents are carrying.
We require all couples who intend to use PGD to see a genetic counsellor prior to proceeding with their IVF cycle. We want you to be sure this is the correct option for you. We want you to have a good understanding of the condition you are testing for and to identify the correct tests to be completed. Some of these tests are not available locally and can require either you or your embryos to travel to another laboratory for testing.
Who May Benefit From PGD?
- Couples with known, testable genetic disorders, or previous children with chromosome abnormalities.
- Women over the age of 40, who have a higher risk of chromosomally abnormal embryos
- Couples who have repeatedly not achieved an IVF pregnancy for no known reason
If you or your partner have any questions, please phone Fertility Solutions on (07) 5478 2482.