Preimplantation genetic testing for aneuploidies, commonly referred to as PGT-A in the IVF language, is performed on embryos to select those who have a better chance to produce a healthy pregnancy. PGT-A requires a small piece of the embryo which is biopsied by the embryologist typically on day 5 or 6 of embryo culture and the geneticists will perform a test to evaluate the quantity of genetic material belonging to the embryo.
This will ultimately identify embryos with the correct number of chromosomes, namely euploid embryos, against those harboring genetic abnormalities (with a missing or an additional chromosome) namely aneuploid embryos. Euploid embryos have of course a better chance to implant. Aneuploid embryos will not result in a successful pregnancy or they may lead to miscarriages or to the birth of a child with a genetic condition.
Aneuploidy is well known to increase with female age. At 35 years of age approximately half of the embryos tested are aneuploid, this rate is increased up to 60% at 38 years of age. Therefore, although PGT-A is suitable for all women undergoing IVF clinics in Turkey to select for euploid embryos, PGT-A may be more advisable for women above 35 years of age.
Advantages of PGT
It allows a clear selection of embryos (as analyzing cleavage patterns in Embryoscope is totally subjective since it very much depends on the laboratory conditions and embryologist’s experience). It should be noted that many aneuploid embryos do divide normally giving rise to high quality embryos. Therefore, PGT is strongly advised in case of:
▪︎ Advanced maternal age (as aneuploidy in embryos is totally correlated with maternal age)
▪︎ Repeated implantation failures
▪︎ Repeated spontaneous abortions
▪︎ History of abnormal fetal karyotype
Disadvantages of PGT
- A biopsy sample representing a very small part of the 5th day embryo, named as blastocyst, has to be taken in order to do the test. Although very simple in unexperienced hands, this procedure can be lethal to the embryo.
- To give time to the genetic test, blastocysts are frozen by a technique called vitrification, which is very straightforward but harmful in unexperienced hands.
- PGT is an expensive test, therefore it may be useful to use it in combination with Embryoscope to prioritize embryos when there are many.
Reference: Homer, H. A. (2019). Preimplantation genetic testing for aneuploidy (PGT‐A): The biology, the technology and the clinical outcomes. Australian and New Zealand Journal of Obstetrics and Gynaecology, 59(2), 317-324.