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.