The topic of PGT has gained a lot of interest in the past few years. The technology is fascinating but the question is whether it's implementation is necessary for all IVF patients. All of the facts stated in this article will be my opinion on this subject. However, these will not be guidelines that should be used for everyone as infertility is very diverse and treatment plans should be personalized.
I'll start with a brief description of what PGT is and how it's done. PGT is when a small biopsy of an embryo is analyzed for genetic abnormalities before that embryo is transferred into the uterus. There are two major types of PGT, one is PGT-A (pre-implantation genetic testing for aneuploidy) and the other in PGT-M (pre-implantation genetic testing for monogenic disorders). The aim of PGT is to identify and transfer an embryo that is genetically normal.
PGT-A is designed to look at chromosomal number of the embryo. We as humans have 46 chromosomes, 23 from our mother and 23 from our father. Sometimes during replication and other cellular processes, the chromosome number of an egg or sperm might deviate from the normal 46 chromosomes. The resulting embryo could be effected by this and have an abnormal number of chromosomes. For example, down's syndrome is a result of an extra chromosome number 21. Aneuploidy refers to the abnormal number of chromosomes. Another example, is an extra chromosome number 8 which has been linked to contribute to miscarriage of an embryo in the first trimester. Now, any person undergoing IVF could opt for PGT-A testing of their embryos. This might seem like a great idea however, it has to be noted that the embryo has to withstand a lot of stress that is imposed from the biopsy. There are many reasons why a patient would undergo PGT-A on their embryos including but limited to: recurrent implantation failure, history of miscarriage, history of chromosomal abnormalities in the family, and possibly those with advanced maternal age. PGT-A is also used for sex selection of embryos. In some countries, sex selection is illegal so this is important to discuss with your specialist. Again, PGT-A can be offered to anyone undergoing IVF but the costs and benefits should be discussed thoroughly with the clinical team to reach the best possible decision. Your specialist as well as the embryologists will be able to guide you to make the best possible decision.
PGT-M will look at abnormalities for a specific single gene which causes a disease/disorder. This is usually offered to patients who either have a history of a certain disease in their families or if one of the two partners suffers directly from a disease. PGT-M is not routinely offered for all IVF patients because there has to be a specific gene that is in question to be looked at. This is one of the reasons why it is important for donors to be honest about their family history of disease. It allows transparency for the recipient and they also have the option of testing their embryos if they choose that specific donor. PGT has revolutionized the field of IVF but there needs to be certain criteria as to which patients would benefit from it. It should not be blindly offered to all patients undergoing IVF if there is no reason for it.
The results of a PGT report will indicate whether the embryo in question is normal, abnormal or mosaic. If the result is abnormal, there will also be a brief explanation as to which chromosomes/genes are effected. What does a mosaic result mean? Basically, an embryo biopsy is comprised of a few cells and all of these cells can be normal or abnormal. In a small number of cases, these cells can represent mosaicism which is when some of the cells are normal and some are abnormal. These embryos could potentially develop to be normal or the abnormal cells could dominate and result in an abnormal presentation. Each clinic will have their own criteria as to which embryos they will and will not transfer. Most clinics have adopted the policy of not transferring abnormal embryos under any circumstances which is most of the time accepted by patients. When it comes to mosaic embryos, there is more of a debate. Some clinics will transfer these embryos and others will not. It is crucial for patients to fully understand the clinics policies before they decide to proceed with PGT. If a clinic will not transfer a mosaic embryo, and that is the only embryo a patient has, they may want to have it transferred in which case they will have to look for another clinic to do their transfer. If all of this is discussed before the procedure, the patient will be more prepared as to what they want to do. The most common policy for clinics is to not transfer abnormal embryos, transfer normal embryos with better morphological features first followed by subsequent normal embryos. In the case of mosaicism, the risks and benefits are usually discussed with the patient and with their informed consent, a decision is made.
Deciding whether or not to add PGT to a cycle of IVF can be daunting so it is important for patients to ask questions and fully understand the process. It is worth mentioning that a normal embryo does not equate to a 100% healthy pregnancy but it will increase the chances. The policies of a clinic should be transparent when it comes to PGT results and patients should seek these before making a decision. Take the time to discuss all of these possibilities with your clinical team and make the best possible decision for you.
