Preimplantation Genetic Testing of Embryos

Preimplantation Genetic Testing (PGT) is an essential component of assisted reproductive technology (ART, IVF) programs. This procedure allows for the detection of genetic abnormalities before the embryo is transferred to the uterus, increasing the chances of a successful pregnancy and the birth of a healthy child.

Main Methods of Embryo Testing

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

• Purpose: Detection of aneuploidies — the presence of extra or missing chromosomes.
• Methods: Utilizes advanced next-generation sequencing (NGS) technologies.
• Sensitivity: High, capable of detecting mosaicism — the presence of cells with different chromosomal sets within a single embryo.

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

• Purpose: Identification of structural chromosomal rearrangements, such as translocations or inversions.
• Methods: Employs technologies that enable detailed analysis of chromosome structure.
• Sensitivity: Depends on the type of rearrangement and the methodology used.

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

• Purpose: Detection of mutations causing monogenic disorders, such as cystic fibrosis or thalassemia.
• Methods: Polymerase chain reaction (PCR) and sequencing.
• Sensitivity: High when a known mutation is present in the family.

Technical Aspects and Sensitivity of Methods

• Embryo Biopsy: Typically performed on day 5–6 of embryo development (blastocyst stage), where a few cells are taken from the embryo's outer layer for analysis.
• Analysis Technologies: Modern methods, such as NGS, provide high accuracy in detecting chromosomal abnormalities and mosaicism.
• Limitations: There is a risk of false-positive or false-negative results, particularly with mosaicism. Additionally, some abnormalities may go undetected due to technical limitations or biological variability of embryos.

⚠ Clinical Aspects and Limitations

• Indications: PGT is recommended for couples with a high risk of transmitting genetic disorders, women of advanced reproductive age, or cases of repeated unsuccessful IVF attempts or miscarriages.
• Limitations: Not all genetic abnormalities can be detected using PGT. There is also a slight risk of embryo loss (in cases of low embryo quality) during biopsy.

The use of PGT enhances the effectiveness of IVF programs, reduces the risk of transmitting hereditary diseases, and increases the likelihood of a healthy child. However, it is crucial to consider all technical and clinical aspects when deciding to use this technology and to consult a geneticist before and after embryo testing.