Advanced embryo selection
Preimplantation Genetic Testing for Aneuploidies
Why undergo genetic testing of embryos?
Each one of us has a genetic blueprint — an ‘instruction manual’ that makes us uniquely human and determines our individual characteristics. This blueprint is contained in almost every cell of our bodies and is packaged into structures called chromosomes. Preimplantation genetic testing for aneuploidies (PGT-A) allows us to test embryos for variations in the number of these chromosomes.
PGT-A involves taking a sample (or biopsy) of a very small number of cells from the outer layer of an embryo at day 5 or 6 of development. From this, we can make predictions about the genetic makeup of the rest of the embryo, helping us decide if they are suitable for transfer. This aids in reducing the incidence of failed transfers, miscarriages, and babies with certain chromosomal abnormalities.
Flinders Fertility has partnered with leading testing laboratories that offer the latest technology to perform PGT-A. Please note that we do not perform PGT-M for single gene conditions or PGT-SR for chromosomal re-arrangements, which can be accessed at other clinics in SA.
What is PGT-A?
PGT-A is a screening test used to determine whether there is an abnormal number of chromosomes in an embryo. In most circumstances, an abnormal number of chromosomes is incompatible with life and if these embryos are transferred, they fail to implant successfully or will miscarry. However, some embryos with chromosome abnormalities can carry through to birth and result in a baby with a chromosomal disorder — the most well-known example being Down Syndrome.
What are the benefits of PGT-A?
By screening embryos for chromosome abnormalities or ‘aneuploidy’, PGT-A can help select chromosomally normal embryos for transfer. Studies also show it may help reduce the average time to pregnancy and reduce the risk of miscarriage in an IVF cycle for patients 38 years and over whose eggs have a higher likelihood of being abnormal due to the normal ageing process.
What are the limitations of PGT-A?
PGT-A cannot change the chromosomal or affected status of an embryo and therefore cannot increase implantation rates.
Furthermore, PGT-A only analyses a small number of cells from an embryo and for a combination of biological and technological factors, it cannot be considered 100% accurate. For this reason, even with a normal test result, we still recommend patients undergo antenatal screening
Risk of harm to the embryo
Embryos are fragile, so any procedure that involves handling the embryo and disturbing its surrounding conditions poses the risk of harm. However, while the risk of harm will always exist, it is thought that the overall risk of damage to the embryo is minimal. The level of risk is also related to how well the biopsy procedure is conducted. Flinders Fertility has experienced and skilled scientists to perform these procedures and they will let you know if they believe it is unsafe to proceed when they assess the embryo before the biopsy.
Mosaicism
When we conduct testing on a sample of cells from the embryo, we are assuming that this sample is representative of all the cells in the embryo. However, it is possible for embryos to contain a mixture of cells (normal/abnormal), due to errors in distributing chromosomes during early embryo development. This phenomenon is known as mosaicism.
When the results for one or more chromosomes come back with an intermediate profile (between normal and abnormal levels) the embryo is labelled as ‘consistent with possible mosaicism’. Technical errors during the testing process can also produce intermediate profiles that appear mosaic when the embryo is fully normal or abnormal. Embryos ‘consistent with possible mosaicism’ generally have a reduced implantation potential and an increased miscarriage rate when compared with embryos that return a euploid PGT-A result. However, this evidence is often changing, so we will provide you with up-to-date information to help you decide if you wish to use embryos with this result.
Results
Not all embryos are suitable for biopsy and must reach a certain stage of development to go ahead with PGT-A testing. Furthermore, once the results are sent back to us they may return as ‘no result’, meaning the test could not determine whether the genetic material of the embryo was normal, or abnormal. This may occur for a variety of reasons.
Your fertility doctor will discuss these limitations in detail with you and provide you with an information sheet. You may require or wish to have genetic counselling to discuss some of these limitations further.
When do I find out the results?
The embryo biopsy occurs within a normal IVF or ICSI stimulated cycle. After the biopsy, the embryo(s) are frozen and the biopsied cells are sent to a laboratory (CooperGenomics) to be tested. Results are usually available in around 3 weeks. The clinical team will review the PGT-A results with you to decide which embryos are suitable for transfer in a frozen cycle. Abnormal embryos are considered unsuitable for transfer and will be removed from storage after you complete the appropriate consent forms.