- What are the different types
of preimplantation genetic testing?
Hello, and welcome to Fertile Minds.
I'm Nikki Kliskey, the PGT coordinator
and one of the senior embryologists
with the Queensland Fertility Group.
Today, we dig a little bit deeper into the types of PGT
to understand the differences between PGT-A,
PGT-SR, and PGT-M.
Preimplantation genetic testing or PGT is the term used
to describe the process of testing embryos for certain types
of genetic conditions.
There are different types of tests that can be offered
on your embryos.
These depend on whether you have a known genetic condition
in the family or if you carry a disease causing mutation
or chromosome rearrangement.
PGT-A is offered to screen embryos
for chromosome copy number
and maybe offered as a compliment
to your infertility treatment.
Today, we will focus our discussion on PGT
that might be required for those that carry
a known genetic mutation.
What is PGT-SR?
If you or your partner have been identified
as carriers of a chromosome rearrangement,
translocation, or inversion,
your doctor will recommend that you have PGT-SR
on your embryos.
SR refers to structural rearrangement.
If you have a chromosome structural rearrangement,
you yourself are otherwise healthy.
But it's very common for men or women
with a chromosome rearrangement to have trouble conceiving.
Some structural rearrangements in men can also be linked
to low sperm counts.
Although individuals with a chromosome rearrangement have
the correct overall number of chromosomes,
the chromosomes are packaged incorrectly.
While this doesn't affect your health,
the chromosome packages in your eggs or sperm may contain
extra or missing segments of chromosome.
This may result in a delay in conceiving
or in recurrent miscarriages.
A translocation can often be inherited
so you may have a family history
of recurrent pregnancy loss.
Can I start PGT-SR treatment straight away?
PGT-SR is recommended so that we can check the embryos
for the correct number of chromosomes.
While this is performed in the same way as PGT-A,
it is important that the genetics lab first review
your karyotype results to ensure that any possible extra
or missing segments are big enough to be detected,
very small segments who may need to be tested
in a different way.
While PGT-SR can identify embryos
with the correct number of chromosomes
and rule out embryos that have an unbalanced copy
of the rearrangement,
the technology cannot distinguish those embryos
that are packaged normally
from those embryos that are balanced
in that they have the correct number of chromosomes
but are also packaged incorrectly like the parent.
So what is PGT-M?
PGT-M is the term used to screen embryos
for monogenic conditions before they're implanted.
Monogenic conditions are diseases that are caused
by a single gene change that is inherited
from an affected or carrier parent.
These mutations may have been identified
by previous genetic testing based on a known family history,
or they may have been identified
by expanded reproductive carrier screening
even when there is no family history present.
So can you start PGT-M treatment straight away?
There is a long list of conditions
that may be tested for with PGT-M.
But as each mutation is specific to an individual or couple,
PGT-M requires the couple to undertake a workup
to design a test that's specific for them.
This process can take between two and six months,
depending on the complexity of the workup.
And this must be completed
before IVF treatment can commence.
A genetic counselor will guide you through this process.
When the workup is finalized,
then you may start your IVF treatment.
So what are we testing for,
and how accurate is this testing?
PGT-M will check your embryos
for the known genetic condition
that has been identified in the parents.
The accuracy of the diagnosis
for this genetic condition is usually around 98%.
We do not check for any other genetic mutations
so we cannot guarantee the birth
of a healthy child following PGT-M.
However, PGT-M will also check the embryos
for chromosomal aneuploidy to ensure the correct number
of chromosomes are present in the embryo.
This is not the primary aim of the test.
And the accuracy of this assessment is typically
between 70 and 90%.
As with all PGT, we recommend prenatal testing
to confirm the results.
What are the risks of PGT testing?
PGT requires your embryos to be biopsied
to remove a small sample of cells for testing.
The process for embryo biopsy in the lab is the same
regardless of what type of PGT treatment you need.
But the analysis of the biopsy sample is different.
Embryo biopsy is an invasive procedure.
The embryos need to be a good quality
with a high number of cells
to go through the biopsy process
without any major compromise.
Poor quality embryos are more likely
to be negatively impacted by the removal of cells.
As embryos need to be frozen to await the test results,
a fresh embryo transfer is not possible
with PGT tested embryos.
As with untested embryos,
not all embryos survive the freeze-thaw process.
The PGT-M experience is different for all couples.
Please get in touch
so that we can discuss your individual circumstances
and answer any questions that you may have.
More information can be found on our website.
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Thanks for watching.