Preimplantation Genetic Testing for Aneuploidies (older name PGS: Preimplantation Genetic Screening)
Preimplantation genetic screening (PGS (PGT-A)) is an examination focused on chromosomal complement of the embryo. Actually, it has been known that formation of embryos with an abnormal chromosomal set is one of the main causes of impaired fertility in human. Such embryos do not implant into the maternal uterus or lead to miscarriages or, in rare cases, to birth of a disabled child.
Using PGS (PGT-A) it is possible to distinguish embryos with normal chromosomal finding from embryos with sporadic (i.e. de novo arisen, non-inherited) "errors” in the number of whole chromosomes or their parts (with so-called aneuploidies). Chromosomally "healthy” embryos are then transferred into the maternal uterus which significantly increases chance of achieving pregnancy and birth of a healthy child.
Indications for examination:
- Advanced maternal age (> 35 years).
- Recurrent miscarriages (twice and more).
- Delivery or abortion of a foetus with a chromosomal abnormality.
- Repeated failure of implantation after previous IVF cycles/embryotransfers (twice and more).
- Significant worsened spermiogram parameters in the partner.
- Using of sperm following TESE (collection of sperm directly from testes) or MESA (collection of sperm from epididymides) for IVF.
- Status post oncology therapy using chemotherapy or radiation therapy in one or both partners.
However, PGT-A can be a part of any IVF-ICSI cycle in the aim to increase the chance to achieve pregnancy and birth of a healthy child, i.e. even when there have occurred none of the indications listed above.
The examination is usually performed on the cells of the trophectoderm extracted on the 5-6th day of the embryo development, but in some special cases it can be performed also on blastomeres or polar bodies.
PGS (PGT-A) by new generation sequencing enables examination of larger quantitative changes (gains or losses) of genetic material within the whole genome, i.e. in all 24 chromosomes.
PGS (PGT-A) by fluorescent in situ hybridization (FISH) is performed usually only for 5 chromosomes and is used rarely based on the indication of a physician.
If you choose to undergo the therapy with preimplantation genetic testing its course will be similar to the "regular" IVF-ICSI treatment. The only difference is that the biopsy (extraction of several trophectoderm cells) is performed on the 5-6th day of the embryo development. The embryonal material is then analysed in the genetic laboratory and the biopsied embryos are vitrified. As soon as the results of the genetic testing are available the IVF-ICSI therapy goes on and ends with the transfer of a healthy embryo.
Genetic analysis and consultation
2019/08/27 IVF Zentren Prof. Zech – Pilsen, RNDr. Martina Hrubá, Ph.D.