Preimplantation Genetic Diagnosis (PGD) and Preimplantation Genetic Screening (PGS) are specialised laboratory techniques that provide diagnostic information concerning an embryo prior to its transfer to the uterus. PGD allows us to assess IVF embryos for genetic defects like Cystic Fibrosis. Traditional screening allows the embryo to be screened for a specific disorder so that only embryos free of the disorder are considered for transfer to the uterus for a chance to establish pregnancy. New screening methods allow us to look at all chromosomes present in the embryo, meaning we can make a more informed decision about which embryo to transfer. Couples who have a serious inherited genetic condition, or a family history of such, or who are at a higher risk of having chromosomal abnormalities in their embryos may consider screening their embryos, for example:
- Patients who are at risk of having a child with an inherited genetic condition eg: haemophilia, thalassaemia, cystic fibrosis, Huntington’s disease, Duchenne Muscular Dystrophy
- Sex linked disorders
- Known history of balanced translocation (a chromosome rearrangement) in one or other of the couple
Karyomapping is a single gene PGD test available in-house. Karyomapping is suitable for patients with a family history of a single gene disorder who are at risk of producing embryos that are affected by that single gene disorder including Cystic Fibrosis, Fragile X, Beta-thalassaemia, or Spinal Muscular Atrophy. Repromed Leading Science
The process of embryo screening
Once fertilisation takes place, the embryo continues to grow and divide until the day of biopsy. On the day of biopsy a special medical laser is used to create a hole in the zona pellucida (which surrounds the embryo like an egg shell) and approximately 5 placental (trophectoderm) cells are removed. The biopsy is done with extreme care and does not cause damage to the embryo. The biopsied embryos are unable to be transferred during that IVF cycle as they are immediately frozen whilst awaiting the screening results (which take approximately 2 weeks).
Only embryos that develop normally in culture are able to be tested for genetic abnormalities, and only embryos that have progressed and are both viable and genetically normal after the biopsy are suitable for transfer. Unfortunately, in some cases there will be no suitable embryos for screening, or no genetically normal embryos following screening, and embryo transfer will not take place.
Preimplantation genetic screening (PGS) allows us to use information about the genetic health of each embryo to select a genetically normal (“healthy”) embryo for transfer. As with all IVF procedures, a successful pregnancy is not guaranteed. However, for many couples who have experienced a serious genetic condition or recurrent pregnancy loss, embryo genetic screening is an advantageous approach for those wishing to maximise the changes of a healthy baby.