Preimplantation genetic testing (PGT) analyzes embryo genetic information. It allows stablishing the chromosomal status of the embryo and identifying those without chromosomal aberrations. Thus, avoiding the transfer of embryos at risk of chromosomal anomalies, contributing to the selection of the embryo with the greatest implantation potential. It is also possible to detect embryos affected by a genetic disease inherited from the parents. The PGT is a tool that helps to select which embryos are suitable for transfer, beyond their morphology.
What is PGT?
Embryo analysis is based on embryonic DNA. This is obtained from one or a few cells extracted, i.e. biopsied, from the embryo. If the biopsy is performed on day 3 of embryo development, when the embryo has between six and eight cells, a single cell is extracted for analysis. If the biopsy is performed between days 5 and 7 of development, when the embryo has reached the blastocyst stage (contains about 200 cells), between 5 and 10 cells are removed.
Can the biopsy affect the embryo development?
If the biopsy is performed by expert personnel and the embryo quality is good, the evolution of these embryos should not be negatively affected. It must be considered that the proportion of biopsied cells is higher on day 3 than in blastocyst (1 of 6-8 compared to 5-10 of 150-200), so the day 3 biopsy has a greater impact on the implantation potential than the blastocyst stage biopsy. In addition, the benefits of PGT in couples at genetic risk outweigh the possible impact of biopsy on the embryo’s ability to implant.
With respect to blastocyst biopsy, several studies have shown that biopsy at this stage does not affect embryonic development and subsequent implantation. In fact, the implantation potential of a blastocyst without chromosomal abnormalities (normal or euploid) is about 70% compared to about 40% of an undiagnosed embryo (Yang et al., 2012).
As with any manipulation process, a possible risk of damage during the process cannot be completely ruled out. According to Reprogenetics data, this figure is estimated to be less than 0.5%.
What is the future?
Currently, in order to carry out PGT, it is necessary to have a sample that is the maximum representative of the embryo, without compromising its viability. Embryo biopsy, although an invasive technique, is safe, and performed by experts and on good quality embryos does not adversely affect embryo development.
The challenge we have to face at is to carry out a genetic analysis of the embryo by means of a non-invasive procedure, which should make it possible to analyze the genetic information accurately without manipulating the embryo (see https://www.reprogenetics.es/es-posible-realizar-un-test-genetico-preimplantacional-sin-biopsiar-el-embrion/ ). For the time being and pending more evidence and studies, trophoectoderm biopsy continues to be the technique that provides the best results for carrying out a genetic test on the embryo.