- How can preimplantation genetic testing
be used to improve your fertility outcomes?
Hello, and welcome to Fertile Minds.
I'm Nikki Kliskey, the PGT coordinator
and one of the senior embryologist
with Queensland Fertility Group.
Preimplantation genetic testing
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 will depend
on whether you have a known genetic condition in the family,
or if you carry a disease causing mutation,
or chromosome rearrangement.
These types of testing
will be discussed in another Fertile Minds video.
Embryos can also go through genetic testing
to screen for aneuploidy.
This type of testing, referred to as PGT-A,
is used to identify and exclude embryos
with the wrong number of chromosomes.
So, what is aneuploidy?
Aneuploidy refers to the wrong number of chromosomes.
We should have 23 pairs of chromosomes.
These a numbered from one to 22,
plus a pair of sex chromosomes,
two Xs for a female, and an X and a Y for a male.
When an extra or missing chromosome occurs in your embryo,
there are three potential outcomes.
Firstly, and most commonly,
this embryo does not form a pregnancy.
If a pregnancy is established,
it is highly likely to miscarry.
Usually, the miscarriage occurs in the first trimester.
Finally, there are a few known chromosomal abnormalities
that can carry to term,
and a woman can give birth to a baby with disabilities.
The most common example of this is Down Syndrome.
What are the indications for using PGT-A?
The most common indications
for testing your embryos for aneuploidy
are advancing maternal age, recurrent miscarriage,
or recurrent implantation failure.
We know that fertility declines with female age.
This decline is a result of chromosomal aneuploidy
in the egg.
After 36, women are more likely to have embryos
with some type of chromosomal abnormality,
than to create normal embryos.
By checking the embryos prior to implantation,
it is possible to rule out those embryos
that are not going to result in a successful pregnancy.
In addition to advancing maternal age,
your doctor might discuss PGT-A with you
if you've had multiple failed embryo transfers
or recurrent miscarriages.
This can be used as a diagnostic tool to help to understand
if the reason for your infertility is related to the embryos
or to the endometrial environment.
Who would benefit from aneuploidy screening?
PGT-A won't be right for everyone.
Ultimately, it's important
to balance up the possible diagnostic benefits
and improve time to pregnancy
against the risk of an invasive embryo biopsy procedure,
embryo freezing,
and the additional costs of genetic testing.
The number and quality of your embryos
will also be significant in determining benefit.
How is embryo biopsy performed?
Embryo biopsy occurs at the blastocyst stage
on day five or day six of embryo development.
A small hole is created in the zoner,
the shell around the outside of the embryo,
and a pipette is inserted through the hole
to apply suction to the outer layer of cells,
the trophectoderm, which are the pre placenta cells.
This is done at an area of the embryo
that is away from the inner cell mass.
The ICM are the group of cells
that go on to become the baby.
A sample of five to 10 cells is removed from the embryo
by aspirating it into the biopsy pipette.
A laser is then used to separate the biopsied cells
from the rest of the embryo.
These cells are then transferred to a tiny test tube
and transported to the genetics lab for analysis.
Embryos are frozen the same day to await the results,
and can be transferred
in a subsequent frozen embryo transfer cycle.
Results typically take two to four weeks.
What type of information will you receive?
Typically, results can be broken down into three categories.
NAD or normal will indicate that no chromosomal abnormality
has been detected in the embryo biopsy sample.
Aneuploid suggest that one or several missing
or extra chromosomes
have been identified in the biopsy sample.
There's also a result called mosaic,
and mosaic results suggest that the biopsy sample
contains both normal and abnormal cells.
It occurs in approximately 5% of biopsied embryos,
and it's not linked to maternal age.
Mosaic embryos, if transferred,
have a lower rate of pregnancy
and a higher rate of miscarriage.
However, some mosaic abnormalities while best avoided,
others can be transferred following genetic counseling.
It's also possible that the biopsy results
may be reported as inconclusive,
or that no result was possible.
This is one of the limitations
of working with very small cell samples,
and small amounts of genetic material.
If this happens,
it may be possible depending on embryo quality,
to thor and rebiopsy the embryo.
However, the risks to the embryo increase with each attempt.
What are the risks? Embryo biopsy is an invasive procedure.
The embryo needs to be of 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 impact
by the removal of some cells.
As embryos need to be frozen to wait for the test results,
a fresh embryo transfer
is not possible with a PGT-A tested embryo.
It is possible to transfer an untested embryo,
and biopsy any excess embryos.
As with untested embryos, not all embryos
survive the (indistinct) process.
How accurate is the testing?
PGT-A is performed on a small sample of cells
removed from the embryo, but it is not 100% accurate.
Validation studies have suggested
that the accuracy is approximately 95%.
There's an assumption made
that the results received from the sample of cells
is representative of the entire embryo.
When a full euploid or full aneuploid result is reported,
this tends to correlate 98% of the time.
When a mosaic embryo's reported,
the clinical concordance rate can be as low as 35%.
When a pregnancy is achieved from a PGT-A tested embryo,
prenatal testing is still advised to confirm the result.
So how might PGT-A improve your fertility outcomes?
If you have one of the three
above-mentioned clinical indications,
and a high number of good quality embryos,
PGT-A testing may improve your time to pregnancy
by prioritizing embryos with higher pregnancy potential,
and excluding embryos that will not result in a pregnancy,
or may miscarry.
If you have low embryo numbers or poor embryo quality,
you should discuss the benefits versus the risks
with your doctor,
before deciding if PGT-A testing is right for you.
Thank you for taking the time to watch and listen.
If you have any further questions, please visit our website,
or reach out to Queensland Fertility Group
for more information,
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Thank you.