Preimplantation Genetic Screening & Diagnosis

Preimplantation Genetic Testing

Preimplantation genetic testing allows for the  genetic diagnosis in embryos resulting from assisted reproduction in order to select and transfer only those that are healthy regarding specific genetic conditions.

The test is designed to detect numerical chromosomal abnormalities (Preimplantation Genetic Diagnosis for Aneuploidy Screening–PGS), structural chromosomal abnormalities as well as genetic diseases such as thalassemia and Cystic Fibrosis in cases where parents are diagnosed. (Preimplantation Genetic Diagnosis- DGD)

Preimplantation Genetic Diagnosis for Aneuploidy Screening- PGT-A

Numerical chromosomal abnormalities or aneuploidies are the most common chromosomal abnormalities. They occur relatively frequently in human oocytes, mainly in women older than 40 years, but also in embryos from assisted reproduction. This is the reason that preimplantation genetic testing is applied by many genetic laboratories worldwide and aims to the transfer of only euploid embryos to the uterus.

The improvement of the successful implantation rate, the decreasing rate of spontaneous abortions, the reduced likelihood of abnormal pregnancies and the increased rate of giving birth to healthy children are major advantages of preimplantation genetic screening and support the argument for its utility.

For the preimplantation testing of embryos, Access To Genome applies  Next Generation sequencing (NGS) technology as well as Comparative Genomic Hybridization (aCGH) technology. The above methods allow simultaneous control of all chromosomes over a period of 12 – 24 hours, making embryo transfer immediate and feasible in the same IVF cycle, as opposed to earlier techniques.

Preimplantation Genetic Diagnosis by NGS or aCGH in cases with Parents Carriers of Structural Chromosomal Aberrations

Structural rearrangements are classified as structural chromosomal abnormalities and involve changes in the structure of one or more chromosomes. These aberrations are divided into balanced and unbalanced rearrangements.

Although carriers of balanced rearangements are normal, they are at high risk of having offspring with unbalanced rearangements. The presence of an unbalanced rearrangement involves loss or gain of genetic material with the risk of developing pathological phenotypic characteristics.

Preimplantation genetic diagnosis is indicated in cases of couples where one of the parents is a carrier of a balanced reciprocal displacement, a balanced Robertsonian translocation or an inversion. All the preimplantation genetic diagnosis studies for translocations in couples with recurrent miscarriages show dramatic reduction of the abortion rate.

In Access To Genome, the NGS and aCGH methodologies used in PGD for structural abnormalities are the same as those applied to PGS for aneuploidies. They allow us to select embryos that are not aneuploid due to the rearrangement of the parent and simultaneously, all chromosomes are tested for the presence of numerical abnormalities.