treatments
Pre-Implantation Genetic Testing (PGT)
Pre-Implantation Genetic Testing (PGT – Preimplantation Genetic Testing) is a diagnostic technique that detects genetic and chromosomal alterations in embryos obtained in the laboratory, before they are transferred and implant in the uterus.
This allows reducing the risk of transmitting serious diseases caused by these alterations to offspring.
To perform PGT, an embryo biopsy is required, consisting of removing cells from the outer layer of blastocysts (trophectoderm). These cells are then sent to genetics centres which, using advanced diagnostic techniques, detect the genetic anomalies in question.
PGT can be of three different types:
- PGT-A: for aneuploidy detection. This type of PGT detects imbalances in chromosome numbers, such as monosomies or trisomies.
- PGT-SR: for detection of structural chromosomal abnormalities. This type of PGT detects losses, gains or imbalances at chromosome level, such as deletions, duplications, inversions or translocations.
- PGT-M: for detection of monogenic diseases (caused by a single gene). This type of PGT detects the presence of a specific gene (or mutation) responsible for a particular disease, such as cystic fibrosis, paramyloidosis, spinal muscular atrophy, sensorineural hearing loss, among many others.
Indications:
- Patients at risk of transmitting chromosomal alterations or monogenic diseases to offspring;
- Patients with a history of recurrent miscarriages;
- Successive implantation failures in previous IVF/ICSI cycles;
- Women of advanced maternal age;
- Previous pregnancy with detection of genetic or chromosomal alterations.
Procedure
The first step in initiating a PGT cycle is to perform karyotyping or pre-genetic testing on both partners, depending on the type of PGT to be performed. Only after obtaining the results can the cycle begin.
A PGT cycle always involves performing ICSI to obtain embryos for analysis.
Generally, the procedure consists of ovarian stimulation identical to that of conventional in vitro fertilization – using injectable medication to promote follicular development and maturation and allow for the retrieval of a larger number of oocytes.
Ovarian puncture is scheduled when the follicles reach the appropriate size. On that day, after the collection and denudation of the oocytes, intracytoplasmic sperm injection (ICSI) is performed.
The development of the embryos is evaluated until the blastocyst stage. This can occur between the fifth and sixth day of culture, at which point an embryonic biopsy is performed, which consists of removing some cells from the trophectoderm of the blastocyst. The cells removed from the biopsied embryo are sent for genetic study, and the embryos are cryopreserved.
After obtaining the genetic results, the fate of the embryos is decided:
- Affected embryos will be thawed and discarded;
- Viable embryos (genetically transferable) may be subsequently transferred in a frozen embryo transfer (FET) cycle.
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