PGT-A: Preimplantation genetic testing for aneuploidy
PGT-A is used to detect or confirm de novo numerical chromosomal abnormalities (aneuploidies). Aneuploid embryos are usually unable to implant in the uterus. If implantation does occur, the pregnancy often ends in an early miscarriage. Only in a small number of cases do aneuploidies allow the pregnancy to continue to term. Abnormalities in chromosome number can result in conditions such as:
- Down syndrome (Trisomy 21)
- Patau syndrome (Trisomy 13)
- Edwards syndrome (Trisomy 18)
- Klinefelter syndrome (47,XXY)
- Turner syndrome (Monosomy X)
PGT-A uses next-generation sequencing (NGS) technology to analyze all 24 chromosomes (22 pairs of autosomes plus the X and Y sex chromosomes) as part of comprehensive embryo screening. This enables the detection of chromosomal abnormalities before embryo transfer, supporting more informed clinical decision-making and increasing the likelihood of a successful pregnancy.
PGT-SR: Preimplantation genetic testing for structural rearrangements
PGT-SR is a genetic test performed before embryo implantation that identifies structural chromosomal rearrangements—translocations that are inherited from the parents. This test enables the analysis of the entire genome or selected chromosomal regions of embryos obtained through the in vitro fertilization (IVF) procedure. It is worth noting that carriers of balanced translocations are usually unaware of their condition because it does not cause any specific symptoms. They typically become aware of the problem only when they experience difficulty conceiving. Carrying a balanced translocation may lead to the formation of unbalanced translocations in the embryo, which can result in miscarriage and unsuccessful in vitro fertilization (IVF) attempts. In addition, the child may develop diseases caused by genetic defects. Indications for PGT-SR include the presence of:
- a chromosomal rearrangement carrier status in one or both parents;
- the birth of a child with a chromosomal translocation.
PGT-SR enables the identification of embryos with unbalanced translocations, allowing the selection of those with the best prognosis for normal development and increasing the chances of the birth of a healthy child. PGT-SR is not a test that excludes translocation carrier status. An embryo considered suitable for transfer may be either free of chromosomal rearrangements or a carrier of the same balanced translocation as its parents.
PGT-M: Preimplantation genetic testing for monogenic disorders
PGT-M is a genetic test designed to detect disorders associated with single genes, known as monogenic disorders. The test involves the analysis of the genetic material of embryos obtained through the in vitro fertilization (IVF) procedure. The primary purpose of PGT-M is to reduce the risk of passing a specific genetic disorder on to the child. By identifying disease-causing mutations and transferring embryos that do not carry these mutations, PGT-M increases the chances of a successful pregnancy and the birth of a healthy child. This test screens embryos for specific mutations in individual genes that may cause conditions such as:
- spinal muscular atrophy (SMA),
- cystic fibrosis,
- hemophilia,
- Duchenne muscular dystrophy,
- sickle cell anemia,
- Fragile X syndrome,
- Huntington's disease.
Preimplantation genetic testing vs. prenatal testing – What are the differences?
In genetic diagnostics, in addition to tests performed before embryo implantation, prenatal testing is also available. Although both types of testing are used to detect genetic disorders, they are performed at different stages of development. Preimplantation genetic testing is carried out before the embryo is transferred to the uterus, that is, before pregnancy begins. Prenatal testing, on the other hand, involves examining the fetus during its development in the uterus, while the pregnancy is ongoing.
What causes genetic abnormalities in a child?
The reasons why certain disorders are inherited vary. Numerous studies indicate that individuals with inherited genetic conditions may pass the same genetic abnormalities on to their offspring. The risk of genetic abnormalities in a child is also associated with the mother's age. The older the woman, the greater the risk of genetic abnormalities occurring in the child.
The use of preimplantation genetic testing (PGT) as part of an IVF procedure is possible following a consultation with a doctor. Indications for preimplantation genetic testing include, among others:
- maternal age over 40 years,
- an abnormal karyotype in one or both partners,
- recurrent miscarriages of unknown cause,
- unsuccessful IVF cycles despite the transfer of high-quality embryos,
- a very low sperm count in the semen of a couple in whom previous pregnancies were affected by fetal chromosomal abnormalities,
- carrier status for balanced translocations or inversions in one or both partners,
- carrier status for a mutation in a single gene in one or both partners (in the case of PGT-M).
Preimplantation genetic testing and the chances of a successful pregnancy
After the test results are available, embryos considered suitable may be transferred to the uterus. However, it is important to remember that even if the genetic test results are favorable, this does not automatically guarantee a successful pregnancy and the birth of a child. Embryo implantation and the further development of the pregnancy also depend on other factors, such as the preparation of the endometrium for embryo implantation, the proper functioning of the hormonal system, and the normal structure of the uterus.
Preimplantation genetic testing consists of several key stages, each of which is essential for obtaining reliable information about the embryo's genetic material and achieving a successful pregnancy.
- The first step is the selection of the embryo by an embryologist. Not every embryo that reaches the blastocyst stage on day 5 or 6 of development is qualified for trophectoderm biopsy. Selection is based on both the embryo's developmental potential and the possibility of obtaining a sample of trophectoderm tissue for analysis. Five to six cells are collected from the blastocyst, taking care not to damage the inner cell mass.
- After the biopsy, the embryos are cryopreserved and stored individually.
- The collected cells are stored under sterile conditions and sent to a genetic laboratory.
- Depending on the clinical indication, appropriate genetic testing—such as PGT-M, PGT-A, or PGT-SR—is then performed. The results are usually available after approximately six weeks.
- Embryos that are considered suitable may be thawed and transferred to the patient's uterus, no earlier than during the next menstrual cycle.
Is preimplantation genetic testing safe?
All collected cells are carefully secured and sent to a specialized genetic laboratory. In accordance with the highest and most stringent safety standards, the genetic material is handled and analyzed under sterile laboratory conditions. Preimplantation genetic testing requires a high level of precision, expertise, and experience on the part of embryologists and geneticists. The main advantage of preimplantation genetic testing is its exceptional accuracy in identifying potential genetic abnormalities in embryos. Although procedures such as PGT-A, PGT-SR, and PGT-M are invasive, the highly trained and experienced team at Klinika Bocian effectively minimizes the risk of damage during the collection of material for genetic analysis. Naturally, there is a small risk that an embryo may stop developing or degenerate following biopsy. However, the benefits of performing these tests significantly outweigh the potential risks of complications.
It should also be remembered that, even with the most advanced medical technologies available, it is not possible to completely eliminate the risk of genetic disorders in a child. Genetic testing can identify only a specific group of genetic diseases and abnormalities. However, the use of preimplantation genetic testing can shorten the time needed to achieve pregnancy, reduce the number of in vitro fertilization (IVF) cycles required, and ultimately lower the overall cost of treatment.
