When must it be done?
The pre-implantation genetic test analyses the embryonic DNA to determine the presence of genetic anomalies, whether they are alterations in a single gene, diagnosis of PGT-M monogenic diseases, or structural alterations (missing or on a chromosomal fragment) PGT-Sr, or anomalies in the number of PGT-A chromosomes.
- It is indicated in advanced maternal age, over 38 years old.
- Implantation failure
- Repeated miscarriage (two or more previous miscarriages).
- Severe male factor.
- Couples with previous pregnancies with chromosomal alteration.
- Couple carrying a chromosomal abnormality.
It is not considered to be indicated in young women under 35 years of age, and should be considered in women between 35-38 years of age on a case-by-case basis.
As for ovodonation cycles, according to a recent study published in 2020 in which more than 1000 patients undergoing ovodonation with PGT-a were evaluated, no better results were obtained in the rate of children born compared to cycles without PGT-A.
What are the benefits?
The purpose of PGT is not to transfer embryos that will not implant or that if they do implant will end in miscarriage. It therefore provides us with information for better embryo selection but does not increase the efficacy of the treatment; euploid embryos are not created, but they are selected. A prospective multicentre study was published this year (2), in which a total of 484 women were transferred a single blastocyst that had been biopsied but without knowing the result of the genetic study carried out. The women who had an euploid embryo transferred had a 65% rate of a child born and those who had an aneuploid embryo transferred had a clinical gestation of 24%, but all ended in miscarriage, the rate of a child at home was 0%. It will therefore allow us to shorten the time to achieve gestation, and very importantly to significantly reduce the miscarriage rate. This is of vital importance in older women, as they have a higher percentage of aneuploid embryos. Thus, a 40-year-old woman who receives a blastocyst without genetic diagnosis has a birth rate of 10% but a miscarriage rate of 45-50%. It is therefore considered highly cost-effective to perform PGT-A in this group of women, especially now that its performance does not have such a high economic cost.
If I do PGT-A, the child will be born healthy?
This test is a very early prenatal test, as it allows us to know the eupolydial status of the embryo prior to its transfer, although it is not useful for diagnosing de novo mutations that may occur after implantation, so genetic screening is recommended in the first trimester following the same criteria as for pregnant women who have not undergone this test.
Can the test affect the embryo?
Richard Scott’s group analysed the impact of embryo biopsy at day 3, at which time the embryo is in the eight-cell stage, and the biopsy analysed one of them, and found that its performance decreased the implantation rate by 19%. Therefore, this practice is currently discouraged.
However, trophectoderm biopsy at day 5 does not have this impact at that time the embryo is endowed with between 150-200 cells and the biopsy and analysis of a group of 5-8 cells of the trophectoderm does not affect the implantation capacity. This depends on obtaining the right number of cells at the most optimal moment, i.e., when the blastocyst is expanded.
How long will the results take?
After the biopsy a genetic study is carried out by means of massive sequencing, the results take between 15-20 days, so it is not possible to transfer the embryo fresh. We have to wait for the results of the test, and then the transfer of a single euploid embryo is programmed, either in a natural cycle in normovulatory women or in a substituted cycle in women with irregular cycles or who wish to plan their transfer at a specific time.
The transfer of a single embryo is another of the advantages of this test, thus avoiding the obstetric complications derived from multiple gestations.