PGT-A
◆What is PGT-A?
Preimplantation Genetic Testing for Aneuploidy (PGT-A) is a test in infertility treatment that examines chromosomal abnormalities in fertilized eggs after in vitro fertilization, selects embryos without abnormalities for uterine transplantation, and prevents miscarriages due to abnormalities in chromosome number.
Initially, the FISH method was used, but it had limitations and a limited success rate. Subsequently, the CGH method was introduced, allowing for the examination of all 24 chromosomes using microarrays. Recently, methods using NGS have also emerged, allowing for the detection of mosaic embryos in early-stage embryos. PGT-A is also called Preimplantation Genetic Screening (PGS), screening 23 pairs of chromosomes, providing valuable information to IVF researchers.
One of the causes of failure in infertility treatment is the increased possibility of aneuploidy with age. Chromosomal abnormalities are the most common cause of infertility treatment failure, with the percentage increasing with age, reported in over 60% of blastocysts at age 40 and over 80% at age 43.
Transplanting embryos with chromosomal abnormalities may lead to difficulties in implantation, miscarriage, and fetal growth arrest, causing patients undergoing infertility treatment to face individual concerns.
"Why limit the scope of PGT-A testing?" Quoted from https://www.jsog.or.jp/activity/pdf/pgt-a_shiryo01.pdf
◆Advantages and Disadvantages
Advantages
- Reduced miscarriage risk and increased pregnancy rate
Evaluating the number of chromosomes in embryos before transplantation reduces the risk of miscarriage by excluding aneuploid blastocysts. Implantation of normal embryos improves the pregnancy rate. - Low miscarriage rate and shortened time
The miscarriage rate per pregnancy decreases, reducing unnecessary transplants and potentially shortening the time to pregnancy. - Reduced physical and psychological burden
There is a high potential to reduce the physical and psychological burden associated with miscarriage.
Disadvantages
- Damage to embryos due to cell collection
Damage to blastocysts due to cell collection may reduce the pregnancy rate. - Difficulty in transplanting early-stage embryos
Culturing blastocysts is necessary for testing, making it impossible to transplant early-stage embryos. Transplantation becomes difficult if there are many aneuploid embryos, leading to potential psychological damage. - Possible difficulty in implantation and miscarriage due to damage
Damage during embryo biopsy may result in difficulty in implantation, miscarriage, and potential effects on the child. - Unsuccessful testing or insufficient embryos for transplantation
There is a possibility of unsuccessful testing or no embryos available for transplantation, requiring consideration of the false positive rate. - Inability to determine abnormalities and miscarriage risk
Abnormalities such as triploidy and tetraploidy cannot be detected, and even with a normal diagnosis, there is a risk of miscarriage. - Impact of increased pregnancy rates on retrieval rates
Even with increased pregnancy rates per embryo transfer, there may be no significant difference in pregnancy rates per retrieval.
◆Testing Method
① Progress to the blastocyst stage on the 5th day after fertilization.
② At the blastocyst stage, the embryo has divided into dozens of cells, and a few (3-5) of these cells are removed for DNA and chromosome testing.
③ During testing, embryo growth continues, so freezing is used to stop growth. Normal blastocysts are identified based on PGS results, thawed, and then transplanted.
Quoted from "Why limit the scope of PGT-A testing?"
https://www.jsog.or.jp/activity/pdf/pgt-a_shiryo01.pdf
