Preimplantation genetic diagnosis of embryos

The Preimplantation Embryo Diagnosis (PGD) is a method of studying 24 chromosomes that allows the detection of serious diseases in an embryo obtained by in vitro fertilization before it is transferred to a woman’s uterus.

PGD ​​makes it possible to study the DNA of embryos and to rule out those carrying certain genetic mutations and diseases. It is useful if there is a history of chromosomal or genetic abnormalities.

To avoid genetic risks, you must be examined to determine if you carry genes that can express pathologies. If both parents have pathologies, it is recommended to submit the embryo to a preimplantation diagnosis. If only one of the two parents carries the sick gene, there is no reason to worry: the child will be born perfectly healthy.

With the procedure being carried out on the third day after fertilization, it is necessary to take a cell from the embryo, which does not harm the embryo, and does not in any way hinder the development. The PGD also makes it possible to determine the sex of the unborn child.

Pregnancy, and more, IVF always brings up a lot of questions, some of which, and rightly so, concern the health of mother and child. Thus, in the surrogacy process, next-generation sequencing plays a key role.

Next-Generation Sequencing (NGS) was developed over a decade ago to facilitate the sequencing of large amounts of genomic data. NGS for clinical diagnosis is now widely used, as it allows a panel of disease-associated genes (targeted sequencing) to be analyzed through whole exome sequencing (also known as clinical sequencing of the disease exome), or even by allowing the sequencing of the entire genome.

The NGS method is part of an IVF program with a preimplantation diagnosis. Examinations and preparation of spouses for in vitro fertilization using or not using the NGS method are no different.

The accuracy of tests for chromosomal or monogenic diseases is approximately 99.9%. The diagnostic process is fully automated and therefore guarantees a very high precision result.

The NGS method is recommended in the following cases:

• If the spouses have already undergone several FIV attempts without obtaining pregnancy, and if several pregnancies have not been successful, in the case of early miscarriages. The non-occurrence of pregnancy is often associated with the presence of chromosomal abnormalities in the embryo.
• Preimplantation diagnosis using the NGS makes it possible to select a genetically healthy embryo with a high probability of implantation, and therefore, reduce the risks mentioned above considerably.
• If the next of kin of the spouses suffer from severe hereditary diseases, the NGS method may be the solution.
• Age is also one of the indications for NGS. Indeed, over time, the probability of developing chromosomal abnormalities, especially in women, increases significantly.

It should be noted that the risk of chromosomal mutations (aneuploidy) in the egg does not depend on the method of conception.

Fluorescence in situ hybridization (FISH) is a molecular cytogenetic technique that uses fluorescent probes that bind only to portions of a nucleic acid sequence with a high degree of sequence complementarity.

The FISH technique is most commonly used to determine the chromosomal makeup of the embryo. Unlike the karyotype, it can be applied to interphase chromosomes, so that it can be used on PBs, blastomeres, and TE samples. The cells are fixed on glass microscope slides and hybridized with DNA probes. Each of these probes is specific for a part of a chromosome and is labeled with a fluorochrome.

The FISH method is considered to be an effective preimplantation technique for determining the sex of human embryos while allowing the detection of an abnormal chromosomal copy number, which is not possible via the polymerase chain reaction (PCR).

With age, chromosomal errors occur in human reproductive cells (eggs and sperm), which reduces the chances of pregnancy, leads to miscarriage or implantation failure. PGD ​​using the FISH method carried out as part of IVF allows the healthiest embryos to be selected and transferred into the uterus, which maximizes the chances of implantation of the embryo in the uterus, and therefore of carrying then to give birth to a perfectly healthy baby.