What is PGT (Preimplantation Genetic Testing)?

PGT (Preimplantation Genetic Testing) is a part of the infertility treatment process through IVF (In Vitro Fertilization). It involves analyzing embryos to detect chromosomal and genetic abnormalities.

Today, let’s explore how PGT benefits embryos and improves pregnancy outcomes, what types of PGT are available, and which types are suitable for which individuals.

PGT, or Preimplantation Genetic Testing, is a widely used technique in the IVF (In Vitro Fertilization) process. It involves screening and analyzing embryos at the chromosomal and genetic levels to detect abnormalities.

PGT helps select embryos with the best quality, reducing the risk of genetic disorders before embryo transfer into the uterus. It also increases the chances of a successful pregnancy by improving implantation rates.

Preimplantation Genetic Testing (PGT) is divided into three main types, each serving a different purpose in identifying genetic abnormalities in embryos:

1. PGT-A (Preimplantation Genetic Testing for Aneuploidy)

PGT-A screens all 23 pairs of chromosomes to detect any extra or missing chromosomes. These abnormalities can lead to miscarriage or congenital disorders such as Down syndrome or cleft lip and palate.
This test can also identify the sex of each embryo. PGT-A helps improve implantation rates and reduces the risk of miscarriage by selecting chromosomally normal embryos.

2. PGT-M (Preimplantation Genetic Testing for Monogenic Disorders)

PGT-M detects single-gene disorders that may be inherited from one or both parents. This test is ideal for couples with a known risk of passing on genetic diseases such as thalassemia or hemophilia.
It ensures that only embryos free from these genetic conditions are selected for transfer, helping to prevent inherited diseases in the child.

3. PGT-SR (Preimplantation Genetic Testing for Structural Rearrangements)

PGT-SR is used to detect structural chromosomal abnormalities such as translocations or inversions. These may be carried by one of the parents and can lead to embryo development issues, miscarriage, or failed implantation.
By identifying embryos with balanced chromosomes, PGT-SR helps reduce the chance of miscarriage and increases the likelihood of a successful pregnancy.

PGT (Preimplantation Genetic Testing) can screen for genetic diseases in embryos at the chromosomal level, single-gene level, or more complex abnormalities, including mitochondrial issues. The genetic conditions can be classified as follows:

• Chromosomal screening: To prevent conditions such as Down syndrome and cleft lip/palate
• Gene-level screening: To prevent diseases such as thalassemia and hemophilia
• Mitochondrial-level screening: To detect disorders related to the nervous system and muscles

Scientifically, embryo cells can be categorized and analyzed using PGT through the following methods:

Next Generation Sequencing (NGS)
The NGS method involves analyzing all 23 pairs of chromosomes in the embryo to detect abnormalities such as missing or extra chromosomes. It can screen for conditions like Down syndrome, cleft lip/palate, and other chromosomal abnormalities. This testing helps reduce implantation failure and the likelihood of giving birth to a child with genetic disorders. Only embryos with healthy chromosomal profiles are selected for transfer into the uterus, increasing the chances of a successful pregnancy.

Polymerase Chain Reaction (PCR)
PCR is a technique used to detect gene-level abnormalities by analyzing DNA sequences. It helps identify inherited genetic defects passed from parents to children. This method can screen for single-gene disorders such as thalassemia, ensuring only embryos without those defects are selected for implantation.

Undergoing PGT as part of the IVF process offers significant advantages for patients facing infertility issues. One of the primary reasons for unsuccessful pregnancies is the implantation failure due to poor-quality embryos that cannot properly attach to the uterine lining. There is also the risk of congenital abnormalities or the inheritance of genetic disorders from either parent.

PGT provides highly accurate genetic analysis—up to 99.9% accuracy—allowing doctors to select only healthy, chromosomally normal embryos before embryo transfer. This screening helps reduce the risk of having a child with genetic conditions and significantly increases the chances of a successful pregnancy.

PGT is beneficial for all individuals undergoing IVF, as it helps screen for genetic abnormalities in embryos at both the chromosomal and gene levels.

• Patients who have experienced two or more miscarriages, which may be caused by chromosomal abnormalities in the embryos.
• Women aged 35 and above, as increased maternal age is associated with a higher risk of chromosomal abnormalities in embryos.
• Individuals with a family history of chromosomal disorders, whether on the maternal or paternal side.
• Couples who have undergone multiple unsuccessful IVF attempts.
• Couples who are carriers of genetic disorders.
• Parents with hereditary conditions that can be passed on to their children at the gene level, such as thalassemia.

After embryos are created through the IVF process, they are cultured in a laboratory until they reach the blastocyst stage, which is the optimal stage for implantation. At this stage, the embryo has developed into more than 100 cells and consists of two parts: the inner cell mass, which will become the fetus, and the trophectoderm, which will develop into the placenta.

A small number of cells from the trophectoderm are carefully biopsied for genetic testing. This procedure does not harm the embryo. The genetic material from these cells is analyzed to examine all 23 pairs of chromosomes, including sex chromosomes, and to screen for genetic disorders.

The results are highly accurate—up to 99.9%. Therefore, PGT is highly recommended for patients undergoing IVF, as it helps identify the most viable and healthy embryos before transferring them into the uterus, thereby increasing the chances of a successful pregnancy.

1. Does the biopsy (removal) of embryo cells affect the embryo?
Removing cells from the embryo for chromosome testing may potentially affect the embryo’s development. However, the risk is very low because only 1-2 cells are taken from the embryo for testing. Currently, there have been no reports of embryo abnormalities caused by this cell biopsy.

2. Is PGT always accurate?
Based on medical and laboratory testing, chromosome screening of embryos using PGT is highly accurate. Studies show that the chance of incorrect chromosome results is less than 1%.

3. Can PGT test for all genetic diseases?
Currently, there are many genetic diseases that PGT cannot cover due to the complexity and variability of gene structures and abnormalities. Therefore, not all hereditary diseases can be detected by PGT at this time.

PGT (Preimplantation Genetic Testing) is a process of analyzing the chromosomes of embryos during in vitro fertilization (IVF). This method is used to detect genetic abnormalities and analyze genetic diseases in embryos. PGT can be divided into three types:

• PGT-A: Testing all 23 pairs of chromosomes
• PGT-M: Testing single-gene mutations
• PGT-SR: Testing for chromosomal structural rearrangements

The purpose is to select the highest quality embryos before transferring them into the woman’s uterus. This process helps reduce miscarriage rates, lowers the risk of genetic abnormalities and diseases, and increases the chances of a successful pregnancy.

If you have any questions, please contact us via Line Official at @BeyondIVF