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What is Preimplantation Embryo Genetic Testing or PGT-A?
One of the reasons for the failure of an IVF program often use to be a genetic disorder in the embryo. Today, we have the opportunity to predict it and successfully transfer chromosomally healthy embryos. Chromosomes are DNA and protein structures that encode genetic information. Normally, each of us has 23 pairs of chromosomes (46 chromosomes). One copy of each pair of chromosomes is inherited from the mother and the other from the father. Abnormalities in the early development of a sperm, egg or embryo can result in the embryo having the wrong number of chromosomes. These multicellular chromosome abnormalities are called aneuploidy. An embryo with a normal set of chromosomes is called euploid (chromosomally healthy), an embryo with a broken set of chromosomes is called aneuploid. It is strictly not recommended to transfer aneuploid embryos into the uterine cavity.
PGT-A is a procedure that allows us to determine the chromosomal status of embryos in the IVF program by screening all 23 pairs of human chromosomes. Only embryos with the correct number of chromosomes will be able to implant and develop into a progressive pregnancy. It is PGT-A that allows you to confidently transfer one embryo into the uterine cavity, because previously, before the appearance of PGT-A in 2014, reproductive specialists often transferred exactly 2 embryos, not having confidence that they are chromosomally healthy and will be able to implant.
What are the indications for PGT?
· Genetic risk of developing aneuploid embryos (genetic diseases in one of the parents or close relatives)
· Reproductive age of a woman older than 35 years (with age, the frequency of incorrect cell division increases, a woman’s age is directly correlated with genetic changes in the embryo)
· Reproductive age of a man over 40 years
· Repeated abortions
· Unsuccessful previous embryo implantations
· Previous unsuccessful IVF programs
· Low sperm quality in a man
Does the genetic status of the embryo depend on the age of the woman?
We know that not all oocytes obtained during aspiration are mature (stage MII), and accordingly not all have a prospect for fertilization.
Unfortunately, already at the age of 22, 20% of oocytes are aneuploid, and at the age of 40, this indicator increases by 80%. At a young age, the oocyte contains the most energy in the mitochondria, which provides the possibility of distribution and transmission of the correct set of chromosomes and the correct fragmentation of embryos. With age, the quality of oocytes significantly decreases (due to the fact that the energy reserve in the oocyte, which they received during intrauterine development, is not restored, but rapidly decreases). Therefore, age is directly correlated with the number of euploid embryos. Chromosomal abnormalities can occur in women of any age, but the chances increase with maternal age. Specific data is provided by the American Association of Reproductive Medicine – ASRM.
If in women younger than 35 the rate of euploid embryos (with the correct set of chromosomes) is 48.2%, then at the age of 35-37 this rate drops to 43%, at 38-40 years – 33.1%, and at 41-42 years, it is already equal to 17%. And at the age of 42 and older, the number of euploid embryos will be only 10.6%, that is, in a woman at the age of 42, out of 10 euploid embryos ready for transfer into the uterine cavity, there will be only 1.
How is PGT-A performed and does it harm the embryo?
In order to perform PGT-A, embryologists take several cells (5-7) from the trophectoderm (cells of the future placenta) of an embryo at the blastocyst stage (5 days of development). At this stage, the embryo has about 100-156 cells, and taking a few of them does not harm it in any way, since the cells that are sent for analysis are part of the future placenta and are not critical for the growth and development of the embryo.
Does PGT-A increase the chances of pregnancy?
Thus, conducting PGT-A significantly increases the effectiveness of the IVF program, although it does not give a 100% guarantee, but it significantly reduces the risks of unsuccessful implantation of the embryo into the uterine cavity and excludes cases of early termination of pregnancy due to chromosomal factors. In comparison with IVF programs in which PGT-A is not performed, the effectiveness of one PGT-A embryo transfer increases twice. There are chromosomal disorders in which the embryo is not even able to implant, because usually the most frequent reason for early termination of pregnancy is the chromosomal factor. Aneuploidy is responsible for the vast majority of first-trimester abortions.
Advantages of PGT-A:
• A higher chance of embryo implantation for transfer into the uterine cavity
• Higher probability of pregnancy
• Reducing the probability of abortion
• Fewer IVF cycles are needed to get pregnant
• Reducing the time until the onset of a progressive pregnancy and the birth of a healthy child
• Increasing the chances of having a chromosomally healthy child
• Significantly lower risk of pregnancy with developmental disorders