What is PGT-A or Preimplantation Genetic Testing for Aneuploidies?
PGT-A or preimplantation genetic testing for aneuploidies is a test performed on embryos (eggs that has been fertilized with sperm) during an IVF (in vitro fertilization) cycle, with the aim of either:
- Screening and reducing the risk of babies being born with chromosomal abnormalities such as Down Syndrome, Patau Syndrome, Edward Syndrome, Turner Syndrome or any sex-linked diseases.
- Increasing the chances of getting pregnant via IVF, while also lowering the risk of miscarriage throughout pregnancy.
PGT-A was previously known as PGS or preimplantation genetic screening. Some fertility specialists or clinics may still refer to the test as PGS. Essentially, both PGT-A and PGS refer to the same test.
What are chromosomes and aneuploidies?
Chromosomes refer to the structures in our cells that carry our genes. The genes in our chromosomes make us who we are. They determine all the things we can see from the outside, such as the colour of our eyes or our gender, and even what happens inside our body, such as the size of our hearts or our metabolism rates.
Each person has a total of 23 pairs of chromosomes in their bodies, totalling up to 46 chromosomes. The 23rd pair is also known as the sex chromosomes (XX for females and XY for males).
Each pair should only contain two chromosomes. However in certain instances, there may be an extra chromosome (known as trisomy), or even a missing chromosome. This rare occurrence is known as aneuploidy.
Aneuploidies can be detected before a baby is born. In fact, with PGT-A, aneuploidies can even be detected before a woman gets pregnant, in embryos that have not been implanted into the womb.
A common aneuploidy is Down Syndrome or Trisomy 21, in which a baby is born with three chromosomes of 21. Babies born with Down Syndrome commonly experience intellectual and developmental problems. Some might be milder, while others may be moderate or even severe.
How does PGT-A increase the IVF pregnancy rates?
Aneuploidies are responsible for a large proportion of miscarriages, including those that occur after an IVF cycle. In fact, studies have shown that more than 70% of spontaneous miscarriages are caused by chromosomal aneuploidies. These abnormalities are problems that cannot be detected under the microscope.
Hence, by performing PGT-A during an IVF cycle, embryologists and fertility specialists are able to detect aneuploidies early in embryos. Thus, we would be able to know which are the viable embryos that should be transferred into the womb, in order to reduce the risk of implantation failure or miscarriage.
Who needs PGT-A?
PGT-A is not a compulsory test for all couples who undergo IVF. However, if you experience any of the following, you may most likely benefit from PGT-A:
- A woman over 35 years of age who is trying to get pregnant via IVF, and want to increase the chances of conceiving (as the risk of aneuploidy increases with the increase in age of the woman who is trying to conceive).
- Previously experienced multiple spontaneous miscarriages.
- Had previously experienced multiple failed IVF cycles.
- Your partner has severe male factor infertility.
- The previous pregnancy resulted in a baby with chromosomal abnormality.
As every couple’s condition is unique, we would advise you to speak to your fertility specialist first if you plan to undergo PGT-A during your IVF cycle.
Benefits of PGT-A
Some of the benefits of the use of PGT-A in couples who are undergoing IVF are:
- Ensure that an euploid embryo (containing a normal number of chromosomes) is transferred, reducing the risk of chromosomal disorders such as Down Syndrome.
- Improve implantation rates.
- Reduce risk of miscarriage.
- Potentially reducing the need of having to repeat IVF cycles, which in turn shortens the time to achieving a viable pregnancy.
- Improve pregnancy and live birth rates.
How is PGT-A done?
PGT-A is done during the midpoint of an IVF cycle. After an oocyte pick-up procedure is performed, the viable eggs will be fertilized with sperm from the male partner. The resulting embryos will be incubated for 5 to 6 days. Upon reaching this stage, one or more cells will be taken from the embryos and PGT-A would be performed in the IVF laboratory. You do not actually have to be present in the clinic for this test to be performed.
PGT-A can be performed via several techniques, such as fluorescent in situ hybridization (FISH), microarray, and next generation sequencing (NGS). NGS is the newer technique that has been adopted by most fertility clinics today.
Summary
The use of PGT-A in IVF cycles has indeed helped to increase the implantation and pregnancy rates amongst specific groups of couples, especially those with a higher risk of chromosomal aneuploidies. If you are planning to undergo an IVF cycle, do speak to your fertility specialists on the pros and cons of performing PGT-A.
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