Genetic infertility. Preimplantation testing of embryos..
When to genetically test embryos?
Diagnosis of genetic defects is not only carried out before a planned pregnancy. It should be remembered that in some cases, genetic defects only become apparent in the offspring. In this case, preimplantation diagnosis is recommended.
- Embryo diagnosis is justified in specific cases. If there is a suspicion that a genetic factor may be involved in pregnancy failure, there is an age criterion, previous failures, a carrier of a disease by one of the partners, or we are diagnosing a monogenic genetic disease that runs in the family. In this case, in order to do embryo diagnosis, we need to have knowledge of the disease present, i.e. the result of a genetic test in the partners.
Types of pre-implantation testing
Due to the different indications, different types of preimplantation tests are performed. Letter extensions indicate the type of study.
- PGT-A detects structural and quantitative chromosome changes (so-called aneuploidies), e.g. Down's syndrome, Patau's syndrome, Klinefelter's syndrome, Edwards' syndrome, Turner's syndrome. As Prof Jezela-Stanek explains, the majority of embryos with chromosome alterations do not survive, and therefore, many of these diseases do not even have a name, other than descriptive. For this reason, the test result is also descriptive, with a plus if there is extra material in the chromosome structure, a minus if there is missing material and a choromosome number.
- PGT-M is performed if there is a family history of a specific disease, so-called monogenic. In this case, the genetic material of the embryo is analysed for mutations of a single gene, e.g. spinal muscular atrophy, cystic fibrosis. PGT-M testing can be combined with chromosome evaluation.
- PGT-SR, on the other hand, is a structural analysis of chromosomes and is performed if we have a suspicion of a structural aberration, such as a Robertsonian aberration. It may not cause symptoms in the parents, but can affect the health of the offspring. Embryos that show abnormalities are not recommended for transfer.
- Each situation is discussed during the visit to the geneticist. Sometimes an abnormality is identified in a mosaic form, there is an error in some of the cells. It is then a topic for discussion whether to use such an embryo. Recent publications state that such a transfer often ends well. However, the risk is lower only when the mosaicism is below 40%, above 80% the risk is high, explains Prof Jezela-Stanek.
Non-invasive embryo study Embrace
For embryos to be suitable for invasive testing, they should be of a good grade. If the embryos are inferior, the test is not performed.
A recent innovation in the preimplantation diagnostics market is the examination of the Embrace. InviMed was the first infertility clinic in Poland to introduce this test.
- It is an alternative to invasive embryo testing. During the examination, we do not obtain cells, but a genetic analysis of the fluid in which the embryo develops is performed. The fluid is taken for diagnosis and an assessment is made in the laboratory regarding the number of chromosomes, the structure," explains Prof Jezela-Stanek.
Based on the data obtained, an embryo euploidy rate is determined using a special algorithm, which will be used to inform the priority of embryo transfer. This study promotes safer and more effective procedures in vitroavoid embryo biopsies.
Consultation: Aleksandra Jezela-Stanek, MD, PhD, Professor IGiChP, InviMed clinic in Katowice.
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