Preimplantation Genetic Testing – Aneuploidy – (PGT-A)

It is a method used to detect chromosomal abnormalities in embryos. This method is ideal for cases of recurrent pregnancy loss, repeated embryo implantation failures in IVF, severe male factor infertility, genetic causes such as translocation carriers, or to shorten the time to pregnancy by selecting among embryos. The procedure involves taking a biopsy from the embryo.

When the embryo reaches the 5th or 6th day, it is called a blastocyst. After taking 5-10 cells from the trophectoderm, which will later develop into the placenta, it is analyzed in the Genetic Laboratory using next-generation sequencing (NGS) to determine the number and structure of chromosomes. NGS technology is more sensitive compared to the older Array-CGH method.

This method can detect mosaic embryos with levels ranging between 20% and 80%.

Normal (euploid embryo): An embryo is considered normal if it has two copies of each chromosome and the sex chromosomes are XX or XY.

Abnormal (aneuploid embryo): An embryo is called abnormal if it has a single copy, three or more copies of any chromosome, or if there are numerical or structural abnormalities in the sex chromosomes.

Mosaic embryo: Sometimes, the number of copies in one or more chromosomes in an embryo should be 2, but it can be observed at a rate between 1-2 or 2-3. These intermediate values are expressed as percentages and are defined as mosaicism in the embryo. The decision to evaluate this embryo is discussed based on the percentage of mosaicism and the patient’s medical history and condition.

Preimplantation Genetic Testing – Structural Rearrangements (PGT-SR)

Even if the mother or father appears healthy, a chromosomal difference present in their structure can be negatively passed on to embryos. One such condition is 'translocation.' There are two different types of translocations: reciprocal, where two or more chromosomes exchange segments with each other, and Robertsonian, where two chromosomes fuse end-to-end to appear as a single chromosome.

An individual who is a balanced translocation carrier may be completely healthy, but if their egg or sperm carries an unbalanced translocation, it can be passed to the embryo as a chromosomal abnormality. This condition can prevent pregnancy or lead to miscarriages.

Depending on the size of the exchanged chromosome segments or the region where they are located on the chromosome, analysis can be performed using Next Generation Sequencing (NGS). Translocation carrier status rises up to 3% in couples with recurrent implantation failures and up to 10% in couples with recurrent miscarriages.

The identification of abnormal embryos through preimplantation genetic testing and the transfer of normal or balanced embryos significantly improves pregnancy success rates.

Although the chance of finding a normal or balanced embryo is low, pregnancy rates achieved through treatments resulting in transfer are quite high. PGT increases pregnancy rates and reduces pregnancy losses in this patient group.

Preimplantation Genetic Testing – Single Gene Disorders

There are diseases with familial genetic inheritance characteristics. Genetic disease screening in embryos through IVF prevents transmission to subsequent generations and also contributes to the formation of a healthy pregnancy.

The procedure performed to understand this is referred to as PGT-M. In the first step of this treatment, the region of the genetic mutation is identified. Then, biopsies taken from embryos obtained through IVF are evaluated in the genetic laboratory for both the genetic mutation and numerical and structural chromosomal abnormalities. This ensures that a genetically healthy embryo is transferred and that the embryo is chromosomally normal.

It is recommended for couples who have a genetic disease or have been identified as carriers and want to have healthy children. Since the risk of disease is high in children of couples diagnosed with single-gene disorders or chromosomal abnormalities, it is frequently applied nowadays.