Understanding Pre-implantation Genetic Testing (PGT)

Understanding Pre-implantation Genetic Testing (PGT)


What is Pre-implantation Genetic Testing and should this be part of my IVF plan?

Pre-implantation Genetic Testing (PGT) is the process of removing a few cells from the part of the embryo that is destined to become the placenta (this is called embryo biopsy), and sending these cells to a specialized lab where the DNA contained is processed and tested.

The most common type of PGT is PGT- A,  (where A is for “aneuploidy,” meaning the embryo has an extra or missing chromosomes or small piece of chromosomes). Aneuploidy is the most common reason for an embryo to fail to implant, or for a pregnancy to end in miscarriage, and the risk increases with maternal age. In theory, by removing any embryos with aneuploidy, we can increase implantation rates, decrease miscarriage rates, and avoid the birth of genetically abnormal babies.  Transferring embryos that have been screened for aneuploidy makes it more likely that a single embryo transfer will be successful, allowing us to transfer fewer embryos and avoid multiple pregnancies and all the complications that come with them.  

Sounds great. Why would anyone NOT want to have PGT-A as part of their IVF cycle plan?

Ideally, PGT-A would be inexpensive and we would be able to obtain this information non-invasively, without removing cells from the embryo (not yet, but it is an area of active research!), the results would be 100% accurate and actionable, and we would always receive results. This is not yet the case. PGT-A is a powerful tool, but it also makes a given IVF cycle more expensive, and the results are >95% accurate, but not 100%.  

Not every embryo grows enough cells to be biopsied, and some embryos could end up being discarded without being tested, even though they could have implanted and become normal babies. Furthermore, sometimes, after biopsy, the report is that some of the cells were normal, but some of the cells were aneuploidy, a condition called “Mosaicism.” Whether or not mosaic embryos should be transferred to patients is still a controversial matter, but the latest reports suggest that while pregnancy rates are lower and miscarriage rates are higher, the resulting babies have been genetically normal, but the numbers are few.

PGT-A is NOT one-size-fits-all and whether it makes sense or not for an individual couple really depends on their individual risk for aneuploidy, their financial situation, religious beliefs, the plan for “what to do if our embryos are mosaic,” etc., and should be discussed case by case with their physician. PGT-A also requires embryo freezing, so cannot be performed on a fresh IVF cycle.

How about PGT-M and PGT-SR?

PGT-M is Pre-implantation genetic testing for mongenic/Single Gene disorders (such as cystic fibrosis or Tay-Sachs), and PGT-SR is Pre-implantation genetic testing for chromosomal structural rearrangements.  These forms of PGT are much less commonly performed, as they are only appropriate for couples with specific genetic conditions.

At Sincera Reproductive Medicine, all forms of PGT (PGT-A,  PGT-M and PGT-SR) are offered.  We welcome you to come in and discuss whether any of these options might be beneficial for you.

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