PGT-A Preimplantation Genetic Testing for Aneuploidy
In Singapore, PGT-A is not offered and not an approved service by the Ministry of Health, Monash IVF Singapore does not offer PGT-A.
You may have also heard it referred to as PGS -Preimplantation Genetic Screening. The PGT-A test is a common add-on test during IVF treatment to determine whether an embryo should be implanted based on its chromosomal number. The purpose of this test is to select embryos with the highest chance of implantation and live birth to maximize your chances of having a baby with each cycle of IVF.
What’s the meaning of Aneuploidy in Genetic Testing?
Pronounced as AN-yoo-PLOY-dee is an abnormal number or alteration of chromosomes in a cell.
What does the PGT-A test for?
PGT-A is a test that allows us (our embryologists and scientists) to examine the chromosomes in an embryo. Usually, each cell in your body has 22 pairs of chromosomes and 2 sex chromosomes (XX or XY). 23 of these chromosomes come from your mother, and 23 come from your father, making 46 chromosomes in total. When an embryo has the appropriate number of chromosomes, it is termed euploid. When there is a deviation from this number due to duplications, deletions, or rearrangements of whole chromosomes or large sections of chromosomes, this is termed aneuploid. Most aneuploidies result in miscarriage or failed implantation, but a few can cause genetic disorders such as Down Syndrome. Embryos can also be mosaic, meaning that some cells are euploid and some are aneuploid.
When undergoing IVF treatment, PGT-A is often recommended as an added test to select the best embryos and minimize your chances of miscarriage. Your eggs have a higher chance of having aneuploidies or mosaics as you age because they have had a longer amount of time in the ovaries to accumulate genetic abnormalities. Thus, test is particularly recommended for women who are trying to conceive over the age of 35 to maximize your chances of successful pregnancy.
How is the DNA analysed?
The technology used to analyse the DNA is called Next Generation Sequencing. Monash IVF Group is proud to offer this cutting-edge technology. The DNA is amplified to millions of copies from a handful of cells and the sequencer then analyses the DNA fragments and compares them to the human genome -the standard map of human genes.
How is PGT-A done?
An IVF cycle is to be completed in order to perform genetic testing on embryos. Once an egg is fertilized in our lab, it is monitored and allowed to grow for 5 days to the blastocyst stage of 70-150 cells. The embryos are frozen while this testing is taking place. Embryos which have grown to Day 5 have cells removed from their outside layer, this procedure is called ’embryo biopsy’. The biopsied cells are sent to the Monash IVF genetics laboratory for testing using Next Generation Sequencing technology.
Monash IVF science and reproductive care at work
While we perform the genetic testing, your embryos are kept frozen and in storage. When we identify embryos with the highest chance of implantation, they’re transferred individually in a frozen IVF cycle. Your remaining viable embryos stay frozen for future use.
What is the meaning of blastocyst? When a normal developing embryo grows to day 5 it reaches the blastocyst stage– A rapidly dividing ball of 70-150 cells. The inner cells will develop into embryos. The outer group of cells will become the cells that nourish and protect them.
How soon will the results be available? It takes between 2-3 weeks to receive your results, after which your fertility specialist can discuss with you which embryos are suitable to transfer (to your uterus). Embryos which have a typical number of chromosomes have the highest chance of implantation (attaching to your uterine wall) and successful pregnancy.
Other types of Preimplantation Genetic Testing
Two other types of PGT may be recommended for you depending on your personal situation.
- Preimplantation Genetic Test for Structural Rearrangements (PGT-SR) may be recommended by your fertility specialist when you have a translocation or misalignment in your chromosomes.
- Preimplantation Genetic Testing for Monogenic (Single Gene) Disorders (PGT-M) test for inherited family conditions caused by single gene mutations, such as those causing Cystic Fibrosis.
It is important to note that PGT-A is a screening tool, not diagnostic test. This means that due to the nature of the test, it can assess your chances of having an embryo implanted with a genetic abnormality, but it cannot give a definite answer, and false positives or negatives may occur.
It is important to discuss your options with your physician or fertility specialist and decide together what is the best choice for you.