Preimplantation Genetic Testing for Aneuploidy
What is PGT-A?
PGT-A (Preimplantation Genetic Testing for Aneuploidy), also known as PGS (Preimplantation Genetic Screening) and CCS (Comprehensive Chromosome Screening), is a test that can be performed on embryos created through IVF and can increase pregnancy rates up to 80%.
For a healthy pregnancy, an embryo requires 46 chromosomes. Chromosomes are small packets of information that contain DNA. Half of the chromosomes come from the sperm and the other half come from the egg. An embryo with the correct number of chromosomes is called a euploid embryo.
Sometimes, embryos can have too few or too many chromosomes. These are called aneuploid embryos. Transferring an embryo with the incorrect number of chromosomes can result in implantation failure, a miscarriage, or a baby with a genetic condition, such as Down Syndrome.
PGT-A is a test that can accurately determine the number of chromosomes in each embryo, so that only embryos with the correct number of chromosomes may be transferred into the uterus.
Who can benefit from PGT-A?
PGT-A is appropriate for most individuals undergoing IVF as it can dramatically improve the chances of a healthy pregnancy.
All embryos have a chance of having an incorrect number of chromosomes. The likelihood of producing these abnormal, aneuploid embryos increases with maternal age. Women over 35 are highly recommended to undergo PGT-A in order to increase the chances of a successful pregnancy.
This procedure is especially encouraged for
- Women who are over 35 years old
- Women who have had repeated miscarriages
- Women who have had repeated failed cycles
The PGT-A Process
PGT-A is done in conjunction with an IVF cycle. On day 5 of embryo culture, the embryo has grown to about 100 cells. Half of these cells will become the baby (called inner cell mass cells) and half will become the placenta (called trophectoderm cells)
To perform PGT-A, a few cells from each embryo are biopsied from the part of the embryo that will form the placenta. The cells that will form the baby remain untouched.
The removed cells are analyzed by our in-house geneticists, using the most reliable technology, to determine which embryos are chromosomally normal or abnormal.
Transfer of Embryos with Improved Chances of Success
Embryos that are chromosomally normal will be selected for transfer into the uterus, which will significantly increase the chances of implantation. The remainder of chromosomally normal embryos can be frozen for potential use in a future cycle.
For each embryo tested, the results will fall into one of the following 3 categories:
All cells have the correct number of chromosomes.
Embryo is suitable for transfer
All cells have the incorrect number of chromosomes.
Embryo is not suitable for transfer
Embryo has a mixture of cells with correct and incorrect number of chromosomes.
May be be considered for transfer if no other euploid embryos are available.
Benefits of PGT-A
- Higher chances of a successful, healthy pregnancy
- Shortest time to pregnancy
- Potentially avoiding time and costs of an extra cycle
- Lower risk of implantation failure
- Lower risk of miscarriage
- More confidence in transferring a healthy embryo without the risk of a genetic condition
Limitations of PGT-A
Abnormal chromosome number is the most common reason for implantation failure and miscarriage. PGT-A can identify chromosomally normal embryos for uterine transfer; however, this does not guarantee a pregnancy. There may be other causes for a failed IVF cycle, such as an unreceptive uterus, or other non-genetic conditions.
Additionally, PGT-A only tests for chromosome copy number and is unable to identify genetic conditions such as cystic fibrosis. For parents with known genetic conditions, PGT-M (Preimplantation genetic testing for monogenic or single gene defects) or PGT-SR (Preimplantation genetic testing for structural rearrangements) may more suitable. Both these tests are offered at CReATe and are performed in our in-house laboratory.
How Long Does It Take?
Our in-house Reproductive Genetics Department provides the fastest results for all genetic testing. PGT-A results may be available in as little as 5-8 days.