Preimplantation Genetic Test (PGT): 5 Basic Questions

In an IVF cycle with Preimplantation Genetic Testing (PGT), the goal is to study the embryos chromosomally before transferring the embryo to the uterus. The IVF cycle proceeds normally until approximately day 5 of embryo development. At that point, a biopsy is performed on the cells in the area that will give rise to the placenta (called the trophectoderm). In other words, a series of cells from that area are collected and sent for genetic analysis. The embryos that have been biopsied are vitrified (frozen) until the biopsy results are available. The time for results can vary from one laboratory to another, but typically, results take about 2 to 3 weeks. Vitrifying the embryos during this time ensures that they do not lose quality.

What will the results of this biopsy indicate? Very important information: which embryos are healthy or chromosomally normal and which are not.

Should you worry about whether your embryos will be damaged in the process? Many patients or couples have this concern, and although there is a small risk, the truth is that professionals and the centers where these tests are performed are experts, so you can breathe easy: the risk of embryos being damaged during the biopsy is really very small.

The genetic study of embryos can be performed for various reasons:

• If there is a genetic alteration in the family (patients carrying serious diseases for their descendants). In this case, PGT-M will be performed for the study of monogenic diseases, i.e., those that affect a single gene.
• In couples where the woman is over 38-40 years old.
• When there is a history of recurrent miscarriages or genetic syndromes.
• After many failed IVF cycles without an apparent cause.
• When there is an alteration in the karyotype (set of chromosomes) of one of the parents.

It is important to note that in women over 40 years old, the rate of altered embryos can be around 80%, so with this technique, the couple can avoid transferring embryos that will not result in a pregnancy or have a higher risk of first-trimester miscarriages.

The genetic report will indicate the result of the genetic study for each embryo. Depending on the result, there are three types of embryos:

• Euploid Embryo: Normal embryo from a chromosomal perspective.
• Aneuploid Embryo: Embryo with alterations in one or more chromosomes. These embryos are not suitable for transfer.
• Mosaic Embryo: Embryo with a percentage of altered cells. Depending on the percentage of cells that are affected, they may be at high risk (non-transferable embryo) or low risk, in which case the possibility of transfer would be considered based on the genetic counseling for each case.

By spanish law, embryos that are not suitable for transfer cannot be transferred to the mother. In these cases, after the patients have signed the informed consent, the clinic must dispose of these aneuploid embryos.

Yes, this possibility is a reality, especially when the reason for genetic testing is the mother’s age. In women over 42 years old, there is a risk that up to 80% of the obtained embryos may be altered, and in the case of women aged 43, the risk increases to 90%. Hence the importance of conducting these tests.