Each cell in our bodies contains our unique DNA packaged into structures called chromosomes. Each set of DNA should be packaged in exactly 46 chromosomes, 23 pairs, like those shown to the left. The numbered pairs, 1 to 22 occur in everyone, while those called X and Y vary between sexes, two Xs for females and one X and one Y for males.
Unfortunately, chromosomes can be lost or extra chromosomes added during egg and sperm production or early embryo development and it is very common for human embryos to end up with an incorrect number of chromosomes (a situation called Aneuploidy).
In most cases these embryos either fail to cause a pregnancy or result in miscarriage (approximately half of all miscarriages are believed to be a result of chromosome errors).
Before PGS can be performed embryos are created in the IVF lab and grown for 5 to 6 days until they reach the blastocyst stage.
A specialized laser is used to make a small hole in the embryo's shell so that it may begin to 'hatch' and a very fine glass pipette is used to take a small sample of cells from the portion of the embryo that will become the placenta. This process is called embryo biosy.
Sensitive genetic techniques (called Next Generation Sequencing or 'NGS') are then used to determine how many chromosomes the sampled cells contain.
It is important to understand that PGS cannot 'fix' any embryos found to be aneuploid, it can only identify them.
This can be beneficial in several ways:
As with every embryo handling procedure there is a potential risk of harm to the embryo.
We are only testing a small sample of the embryo and it is possible that these cells may not be the same as the rest of the embryos, something called Embryo Mosaicism. This can result in a false or unclear test result.
The very small sample we are working with and the variable nature of human embryos also means that we may not be able to obtain a result for some embryos.
If you are considering undertaking PGS speak with your fertility specialist to discuss whether this technique may be of benefit to you.
If you have any further questions a genetic counselor is available to discuss these processes in more detail.