Advances in genetic testing technologies are enabling the study of the genetic composition of embryos prior to implantation with increased accuracy, enabling higher implantation rates and minimizing the risk of a genetic disorder in the offspring.
Recent advances in molecular biology methods have enabled scientists to screen embryos produced by In Vitro Fertilization techniques (IVF) prior to their transfer in the prospective mother’s uterus. Traditionally, embryo screening was performed with morphological criteria – an embryologist would evaluate a series of visual attributes under the microscope. However, numerous studies have shown that morphological characteristics do not correlate with euploidy (the term used to signify that an embryo carries the correct number of chromosomes and is thus genetically suitable for transfer).
Approaches to screen the embryonic genome have been present for many years but it wasn’t until the introduction of technologies such as array Comparative Genomic Hybridization (aCGH) and more recently Next Generation Sequencing (NGS) that enabled geneticists to be able to quickly and reliably study multiple embryos at once and identify any abnormalities, in a test called Preimplantation Genetic Testing For Aneuploidies (PGT-A). These abnormalities appear more often in women of advanced age and can be the cause of recurrent pregnancy loss or recurrent implantation failure.
For such cases PGT-A can be applied with the aim to reduce the time to pregnancy, reduce miscarriages and increase pregnancy and live birth rates, while also reducing the risk of a genetic disorder in the offspring.
PGT-A is a sensitive procedure that is only performed by specialized genetics laboratories and highly trained geneticists. The whole process is orchestrated in close collaboration with the IVF center: the IVF specialist and the embryologist. Specifically, after oocyte and sperm retrieval, fertilization is performed in the embryology laboratory, where embryos will grow for 5 days. At day 5 (blastocyst stage) a few cells will be removed from each embryo and sent to the genetics laboratory, where the genetic analysis will be performed. The embryos are subsequently categorized as suitable for transfer or not suitable for transfer. Results are usually available within 10 working days but can be delivered in as little as 24 hours if the couple proceeds with a fresh cycle. The final report is sent to the IVF center that will perform the embryo transfer.
You can visit a fertility or genetics specialist for further information about PGT-A.
Note: Preimplantation Genetic Testing for Structural Rearrangements (PGT-SR) and Preimplantation Genetic Testing for Monogenic Disorders (PGT-M) are diagnostic approaches that are indicated for couples that are carriers of a monogenic disorder or a structural chromosomal rearrangement in order to avoid the birth of an affected offspring and will be discussed in a separate article.
Anastasios Mitrakos, PhD
Amelia Pantou, MSc, PhD