Preimplantation Genetic Testing
Preimplantation genetic testing (PGT) involves the screening of embryos to detect chromosomal variations or errors. Only embryos that are euploid (correct number and configuration of chromosomes), are then used for embryo transfer. Embryos with an aneuploid (incorrect number or configuration of chromosomes) result are not able to be transferred.
When PGT is indicated, patients undergo all the same process as they would for IVF/ICSI, up until the point of embryo transfer. Once embryos have successfully cultured in the laboratory for 5-6 days, a small number of cells from the outer layer will be collected via fine needle biopsy for testing. The cells that are taken for biopsy are the cells that would later become the placenta (not the foetus) and therefore do not damage the embryo. The embryos are then frozen. Results from genetic testing will be ready and communicated with the doctor and patient/s after about 3 weeks and further treatment planning can proceed.
There are several methods and indications for PGT:
This is the most common type of PGT performed in IVF clinics. The test is designed to identify the correct number of chromosomes and detect some cases of extra or missing segments of chromosomes in the cells of the embryo. This is often indicated for individuals and couples of an advanced parental age, because chromosomal errors increase as age advances. It may also be indicated for people who have had a history of implantation failure or miscarriage with the aim of decreasing the time to pregnancy (see video below to learn more about PGT-A)
PGT-Structural Rearrangement (PGT-SR)
This type of PGT is for people with a known structural chromosomal rearrangement, picked up by a blood test called a karyotype. Embryo testing is performed to detect embryos that have structurally balanced chromosomes so they can be selected for embryo transfer.
PGT-Monogenic Disorder (PGT-M)
Monogenic or single gene disorders are conditions that are inherited and often run in families. They are caused by specific gene changes in DNA. For individuals and couples with a known history of a single gene disorder, PGT-M may be indicated to select embryos that are unaffected by the specific gene changes to reduce the risk of having a child with the condition. Examples of single gene conditions include cystic fibrosis (CF) and spinal muscular atrophy (SMA). Single gene conditions may be known to run in families, or may be picked up by reproductive genetic carrier screening. Medicare rebates are now available for PGT-M.
Sex selection of embryos may be performed when there is a significantly increased risk of a child of a particular sex having a genetic condition. This form of embryo testing is highly regulated and approval to undergo this testing is subject to a review by an independant Patient Review Panel (PRP).