Preimplantation genetic diagnosis
Preimplantation genetic diagnosis (PGD) is a highly sophisticated technique that allows embryos to be tested for specific chromosomal or genetic abnormalities. I am directly involved in the running of the Melbourne IVF PGD program, which is an internationally recognised national leader in PGD development.
I may recommend PGD for couples with long periods of infertility or with serious genetic diseases in the family.
Depending on a woman's age, many embryos created via natural conception or IVF, have a chromosome aneuploidy, which means they have no chance of resulting in a healthy baby.
With PGD, we can make sure that only embryos not affected with the condition being tested for are selected for implantation and pregnancy. The Melbourne IVF program has helped hundreds of couples conceive healthy babies in this way.
How does PGD work?
Cells are removed from an embryo on either day three or five, and are tested for specific conditions such as cystic fibrosis or Down syndrome. Used in conjunction with IVF, PGD maximises the chance of a healthy baby, because only chromosomally normal embryos or those diagnosed as being free of a specific disorder are transferred.
Types of PGD Testing
Advanced Embryo Selection
Advanced Embryo Selection is a sophisticated and innovative procedure that involves full chromosomal screening on all 24 chromosomes in a developing embryo. This allows us to select the embryo with the greatest likelihood of resulting in a healthy baby.
Testing for a translocation
In rare cases, a patient may carry an error called a translocation, where parts of chromosomes break off and are swapped around, or get attached to each other. You may still have a normal complement of chromosomes, but if you have children there is a risk you could pass on missing or extra pieces of chromosome. This is called ‘unbalanced translocation’.
Embryos with unbalanced translocation usually do not implant or will miscarry, but sometimes they are born with severe abnormalities. We can use PGD to test for unbalanced translocations as well as errors of all the rest of an embryo’s chromosomes.
Some genetic conditions, like haemophilia and some types of muscular dystrophy, only affect one gender. PGD can be used to determine the gender of embryos, so that only embryos of the unaffected gender and with the correct number of chromosomes will be used for transfer.
Gender selection is prohibited in Australia for family balancing, or anything other than medical reasons.
Single gene defects
A gene is a sequence of genetic material, or DNA, on a chromosome. Humans have up to 20,000 different genes, arranged on 23 pairs of chromosomes. Each gene has a specific function. When the DNA sequence on a particular gene is altered, a genetic disorder, such as cystic fibrosis, may result.
If there is a single gene defect in your family, the PGD team and I will develop a test for you, so that we can identify which embryos are unaffected.
Some serious genetic conditions – like Huntington’s disease – do not manifest until later in life. People who have (or have had) a parent affected by one of these conditions often do not want to have testing to determine if they have inherited it, but do not want to risk passing it on to their own children.
We can use PGD in this situation. We do not test for the genetic error, but embryos are tested to make sure they have not inherited the ‘at risk’ gene.