PGT-A
◆What is PGT-A?
Preimplantation genetic testing (PGT-A) examines fertilized eggs for chromosomal abnormalities after in vitro fertilization and selects fertilized eggs with no abnormalities for implantation into the uterus, This is a fertility test to prevent miscarriages due to abnormal chromosome counts.
In the early days, the FISH method was used, but it was limited and had a limited success rate. Later, the CGH method was introduced and it became possible to examine all 24 chromosomes using microarrays. More recently, NGS-based methods have been introduced to detect mosaicism in early embryos, and PGT-A, also called aneuploidy preimplantation genetic testing (PGS), screens 23 chromosome pairs and provides valuable information for IVF researchers.
The likelihood of aneuploidy increases with age as one of the most common causes of infertility treatment failure. Chromosomal abnormalities are the most common cause of infertility treatment, with the percentage increasing with age, reported in 60% of blastocysts at age 40 and over 80% at age 43. Transferring an embryo with chromosomal abnormalities can result in difficult implantation, miscarriage, or fetal developmental arrest, and patients undergoing fertility treatment are troubled by each of these situations.
Why limit the scope of PGT-A testing?" Citation. https://www.jsog.or.jp/activity/pdf/pgt-a_shiryo01.pdf
◆Advantages and Disadvantages
Advantages
- Miscarriage risk reduction and pregnancy rate improvement
The risk of miscarriage is reduced by evaluating the chromosome count of the embryo prior to transfer and excluding aneuploid blastocysts if any are present.
Transfer of normal embryos improves pregnancy rates. - Low miscarriage rates and reduced time
Potential to reduce miscarriage rate per pregnancy, reduce unnecessary transplants, and shorten time to conception. - Reduction of physical and mental burden
The physical and emotional burden associated with miscarriage is likely to be reduced.
Demerit
- Damage to embryos associated with cell harvesting
There is damage to the blastocyst due to cell harvesting, and there is concern that the pregnancy rate may decrease. - Early embryo transfer not possible and difficult transfers
Culture to blastocyst is required for testing, which makes early embryo transfer impossible.
If there are many aneuploid embryos, transfer is difficult and psychological damage is possible. - Difficulty in implantation and possible miscarriage due to damage
Damage during embryo biopsy may cause implantation difficulties, miscarriage, and effects on the child. - Unsuccessful tests or lack of embryos available for transfer
There is a possibility that the test may be unsuccessful or that none of the embryos are available for transfer, and the false-positive rate must be considered. - Inability to determine abnormality and risk of miscarriage
Abnormalities such as triploidy and tetraploidy cannot be determined, and miscarriages may occur even with normal determinations. - Increased pregnancy rate affects egg retrieval rate
Possible increase in pregnancy rate per embryo transfer but no significant difference in pregnancy rate per egg retrieval.
◆Method of Examination
①The embryo progresses to a blastocyst on the fifth day after fertilization.
②At the blastocyst stage, the blastocyst has divided into dozens of cells, some of which (3~5 cells) are extracted for DNA and chromosome testing.
③Since the embryos are growing during the test, they are cryopreserved to stop their growth, and the PGS results are used to identify normal blastocysts, which are then thawed and transferred.
Why limit the scope of PGT-A testing?" Citation.
https://www.jsog.or.jp/activity/pdf/pgt-a_shiryo01.pdf
