Clinica Tambre explains that Preimplantational Genetic Diagnosis (PGD) is presented as a solution for the transmission of genetic diseases to offspring. It consists of a series of studies and techniques for analyzing the DNA present in a single embryo cell in an in vitro fertilization (IVF) environment. The embryos resulting from the study that do not present chromosomal or genetic alterations will be transferred to the uterus for gestation.
Preimplantation Genetic Diagnosis is also often used in cases of repeated miscarriages or implantation failures, when the rest of the studies performed in these cases have all been normal and have not detected any problems.
Less frequent cases that also require this genetic study are the selection of histocompatible embryos for therapeutic purposes to third parties. This is the selection of embryos that are compatible with a first-degree relative, and is generally performed to measure compatibility with another child who has been affected by a severe hematopoietic disease and requires an umbilical cord or bone marrow cell transplant. In many of these cases, authorization from the National Commission on Assisted Human Reproduction will be required.
In reference to embryo selection, in Spain it is currently forbidden to select the sex of the embryo for reasons that are not strictly medical.
Preimplantation Genetic Diagnosis (PGD) Procedure
To carry out PGD, the first step is to obtain embryos from an in vitro fertilization (IVF) cycle. These embryos are biopsied three days after the puncture, when a single cell is extracted, or on the fifth day after the puncture, when several cells are extracted.
Once the cells are obtained, they are analyzed according to the technique to be used:
- In the case of the FISH (Fluorescent In Situ Hybridization) technique, the cells are fixed on a slide for subsequent analysis.
- Currently the most commonly used technique is a-CGH (array comparative genomic hybridization), especially for cases of chromosomal or structural alterations, as this technique is much more robust and capable of detecting all chromosomal abnormalities in the cell. In a-CGH, the biopsied cells are transferred to the genetic analysis laboratory in special microtubes. The samples are then processed in the laboratories and, after analysis of the results, the embryos are determined to be suitable or unsuitable, depending on whether they present alterations for transfer.