Part 3-Embryology in the 21st Century: Breakthroughs and Innovations

Preimplantation genetic testing (PGT)

Michael B. Yakass, Ph.D.

Preimplantation genetic testing (PGT)

Imagine there is a particular genetic condition in your family that you want to avoid passing on to your children. That is exactly what PGT tends to solve and this technology has currently revolutionized how the IVF industry is viewed. With the use of PGT, IVF goes over and beyond a service meant to assist infertile couples to have children. There are three main types of PGT, namely; 

1. Preimplantation genetic testing – Aneuploidy (PGT-A)

PGT-A detects abnormalities at the chromosomal level. About 50% of miscarriages are due to chromosomal defects/aneuploidies, i.e., a gain and/or loss of a whole chromosome resulting in monosomies or trisomies or variations other than the normal set of two sister chromosomes. Advanced age women tend to have more chromosomally abnormal embryos, hence PGT-A may be indicated in IVF treatments involving advanced age women. PGT-A is also recommended for couples who have had repeated implantation failures or multiple failed IVF attempts. PGT-A may also be indicated in treatments involving men with high DNA fragmentation index (DFI) as high DFI is associated with failed IVFs and miscarriages. However, PGT-A is not a guaranteed way to avoid miscarriages as there are other possible causes of miscarriages.

2. PGT-M

Some genetic diseases are caused by a single gene disorder, such as Sickle Cell Disease on the haemoglobin beta (HBB) gene, breast cancer risk genes (BRCA1, BRCA2), etc. PGT-M helps to detect such monogenic or single gene disorders in preimplantation embryos made from the IVF/ICSI process. PGT-M is indicated in cases where the couple are carriers for an autosomal recessive trait, or a carrier for an X-linked condition or an autosomal dominant condition. In Africa, the most prevalent condition for which PGT-M is beneficial is to exclude sickle cell disease in carrier couples. 

3. PGT-SR

PGT-SR is beneficial to detect structural rearrangements in the chromosomes such as deletions, inversions, balanced and unbalanced translocations. 

PGT has become an essential innovation in the practice of reproductive medicine due to the ability to exclude particular diseases from offspring(s) of carrier parents. However, no randomized control trial has demonstrated that PGT significantly improves pregnancy rates over cycles without PGT.

4. Ghana

PGT services are currently available in Ghana with some centres resourced with the equipment required for the embryo biopsy process and the next generation sequencing (NGS) platform. The first report of PGT-M use in Ghana to exclude sickle cell disease was reported at the Lister hospital and this caught massive attention in the media. 

In this series of 6 articles, we will take a daily look at some of the most recent advancements and innovations (in no particular order) in this rapidly growing field of medicine.