Preimplantation Genetic Testing (PGT)

Preimplantation Genetic Testing (PGT): Healthy Embryo Selection

Preimplantation genetic testing (PGT) is a comprehensive method describing the process of taking a biopsy from embryos developed in the laboratory during in vitro fertilization (IVF) treatment, examining their genetic and chromosomal make-up, and selecting a healthy embryo before transfer. In situations such as recurrent miscarriage, IVF failure, advanced maternal age, and carrier status for hereditary diseases, it can make a positive contribution to the likelihood of pregnancy. At the clinic of Prof. Dr. Melahat Atasever, PGT is performed in cooperation with specialized genetic laboratories, using current technology.

What Is PGT (Preimplantation Genetic Testing)?

PGT is based on taking a few cells with a micromanipulation technique from fertilized embryos at the blastocyst stage (day 5 or 6) during the IVF process and performing genetic analysis on these cells.

As a result of the analysis, chromosomally normal embryos are identified, and healthy embryos are frozen and transferred into the uterus in a subsequent cycle.

PGT does not treat the embryo; it only helps select the embryo that is genetically healthy. Patients are clearly informed before the procedure that not all embryos may be genetically normal and that in some cases no transferable embryo may be obtained.

Thanks to molecular genetic technologies developed in recent years, all 24 chromosome types can now be analyzed in detail with methods such as NGS (Next Generation Sequencing) and aCGH (Array Comparative Genomic Hybridization).

What Are the Types of PGT?

PGT-A: Aneuploidy Screening

PGT-A examines all 24 chromosome types in the embryo, evaluating the presence of missing or extra chromosomes (aneuploidy).

With this method:

• Down syndrome (Trisomy 21)
• Edwards syndrome (Trisomy 18)
• Patau syndrome (Trisomy 13)
• Other numerical chromosome abnormalities

can be detected. It is one of the most frequently recommended PGT types, especially in advanced maternal age.

PGT-M: Monogenic Disease Screening

PGT-M is an analysis performed to prevent the transmission to the embryo of a specific genetic disease known in the family.

Within this scope:

• Thalassemia
• Sickle cell anemia
• Cystic fibrosis
• SMA (Spinal Muscular Atrophy)
• Huntington’s disease

and similar hereditary diseases can be evaluated.

PGT-SR: Structural Chromosome Abnormalities

PGT-SR is applied in parental structural chromosome abnormalities such as balanced translocation or inversion.

This method offers an important evaluation option especially for:

• Couples experiencing recurrent miscarriage
• Those with recurrent IVF failure

Who Is PGT Recommended For?

PGT may be recommended in the following situations:

• Advanced maternal age over 37
• A history of recurrent miscarriage
• Two or more IVF failures
• Known carrier status for a genetic disease
• Couples carrying a balanced translocation
• A family history of a serious hereditary disease

Prof. Dr. Melahat Atasever determines which type of PGT is appropriate based on a detailed clinical evaluation and genetic history.

How Is PGT Performed? The Step-by-Step Process

PGT is always performed together with the IVF process.

1. Ovarian stimulation: The ovaries are stimulated with medication.
2. Egg retrieval (OPU): The matured eggs are collected.
3. Fertilization: Embryos are created in the laboratory environment.
4. Blastocyst development: The embryos are monitored until day 5-6.
5. Embryo biopsy: A few cells are taken from the trophectoderm (the cells that will later form the placenta).
6. Genetic analysis: The cell samples are sent to the genetic laboratory.
7. Embryo freezing: The embryos are frozen while the results are awaited.
8. Transfer: The healthy embryo is transferred once the uterus is made ready.

With NGS analysis, a map of all the chromosomes is created; the results are generally ready within 2-3 weeks.

What Are the Advantages of PGT?

The important advantages of PGT are:

• Supporting the selection of a healthy embryo
• Potentially contributing to the likelihood of pregnancy per transfer
• Potentially reducing the risk of recurrent miscarriage
• Potentially reducing the number of failed IVF attempts
• Considerably lowering the risk of transmitting a hereditary disease
• Potentially reducing the risk of chromosomal abnormality in advanced maternal age

Especially in couples who are carriers of a genetic disease, being able to prevent the transfer of an affected embryo provides a significant advantage.

Disadvantages and Limitations of PGT

PGT also has some limitations:

• Not every embryo may be genetically healthy
• No transferable embryo may be obtained at all
• The evaluation of mosaic embryos can be difficult
• It can add cost on top of standard IVF
• It may not detect genetic variations that are not targeted

Although modern NGS technologies have considerably reduced the margin of error, no genetic test offers one hundred percent certainty.

Which Diseases Can PGT Diagnose?

The following diseases can be evaluated with PGT:

With PGT-A

• Down syndrome (Trisomy 21)
• Edwards syndrome (Trisomy 18)
• Patau syndrome (Trisomy 13)
• Turner syndrome
• Klinefelter syndrome
• Other numerical chromosome anomalies

With PGT-M

• Thalassemia
• SMA Type 1
• Cystic fibrosis
• Duchenne muscular dystrophy
• Huntington’s disease
• BRCA1/BRCA2 mutations
• Sickle cell anemia

With PGT-SR

• Chromosomal irregularities linked to balanced translocation

PGT in Ankara with Prof. Dr. Melahat Atasever

If you are considering a PGT evaluation due to recurrent miscarriage, failed IVF attempts, or carrier status for a hereditary disease, you can consult Prof. Dr. Melahat Atasever in Ankara.