What you should know about PGD & PGS

If you and your partner have been struggling with fertility issues and are seriously considering In-Vitro Fertilisation or IVF, the consideration of whether you should be undergoing PGD and PGS on top of an IVF can be quite daunting. This is because, in normal IVF procedures, the best embryos are selected based on their appearance and morphology only. Therefore, the genetic content of those embryos or any chromosomal abnormality cannot be detected. However, by undergoing PGD and PGS, you will be able to screen your embryos for any potential genetic and chromosomal issues.  However, before we jump into the band wagon of having PGS or PGD, there are a few things we need to consider.

What is PGS?
PGS stands for Pre-implantation Genetic Screening. In PGS, a cell is taken from an embryo  which was created following an IVF procedure, so that it can be tested for chromosomal abnormalities before the embryo is transferred to the womb. This test will be able to tell us whether the embryo has normal sets of chromosomes. However, it will not be able to tell us whether this embryo has a genetic problem or not.

It is important to note that not all the patients going through an IVF required a PGS. You may want to consider it if:

• You are of advanced maternal age, whereby embryos may show greater levels of chromosomal abnormalities.
• You have had recurrent miscarriages.
• You have had repeated IVF failure.
• Either of you has a chromosome rearrangement.

The PGS procedure involves:
1. You will undergo a normal IVF treatment and your eggs will be collected and fertilised.
2. An embryo is grown in the laboratory for a few days.
3. An embryologist will perform a biopsy and remove a few cells, usually on day 3 or 5.
4. All 24 chromosomes are analysed (22 non-sex chromosomes and two sex chromosomes X & Y).
5. If the embryo is normal, it will be transferred into your womb.
6. Any remaining unaffected embryos can be frozen for later use.
7. Affected embryos will be allowed to perish.

What is PGD?
PGD is an abbreviation for Preimplantation Genetic Diagnosis. In PGD, a cell is taken from an IVF embryo so that it can be tested for a specific genetic condition before the embryo is transferred to the womb. It can be used to test for any genetic condition that is known to be caused by a specific gene.

At present, PGD is used to screen for more than 250 genetic conditions, such as Huntington’s disease, Cystic fibrosis, Thalassaemia, Duchenne muscular dystrophy and Fragile-XPDG to name but a few. Therefore, PGD enables individuals with an inheritable genetic condition to avoid passing it on to their children. The PGD process is more tidious and challenging compared to PGS. It is used to test for a specific genetic disease which is known to your family, i.e. you or your partner is confirmed a carrier of a specific gene at a certain point of the chromosome. You need to bear in mind that by performing a PGD, it does not mean that screening of ALL genetic diseases are performed at the same time. This is because human beings have millions of gene and it is impossible to screen ALL of the genes in one go.

However, not all IVF patients need to undergo PGD. You may want to consider it, or your specialist may recommend it to you if:

• You or your partner (or both) are carriers of single gene mutations.
• You ended a previous pregnancy due to a serious genetic condition.
• You have a child with a serious genetic condition.
• Either of you has a family history of a serious genetic condition or chromosome problems.

The PGD procedure involves

1. You will undergo a normal IVF treatment and your eggs will be collected and fertilised.
2. An embryo is grown in the laboratory for a few days, until it has divided into around 8 cells.
3. An embryologist will remove one or two of the cells from the embryo.
4. The cells are tested to see if the embryo has a gene that causes a genetic condition.
5. If the embryo is free of any genetic condition, it is transferred to the womb.
6. Any remaining unaffected embryos can be frozen for later use.
7. Affected embryos will be allowed to perish.

Since PGD and PGS help detect genetic conditions and chromosomal abnormalities, they help IVF patients to decide if they wish to continue with pregnancy.

The Pros and Cons of PGD and PGS
Before you decide on undergoing PGD or PGS, your fertility consultant will explain their pros and cons to you, which include:

Pros

• They can detect an inherited chromosomal or genetic issues and help prevent passing chromosomal or genetic diseases to the next generations
• They are a form of early detection of chromosomal or genetic problems before the embryo is transferred back into the uterus.
• They help increase a couple’s chances of conceiving a healthy child.
• It allows older women to still have viable children.

Cons

• There is a risk that embryos may be traumatized or destroyed due to damage during the biopsy process.
• There is always a possibility of an undetected disease, as no form of testing can guarantee 100% accuracy
• The test is expensive
• You may not have any embryos to transfer after the IVF & PGD/PGS , which is frustrating for patients because after investing time, money & effort, the result can be disappointing
• There is no guarantee that an embryo which had been screened will definitely get implanted after being transferred into the uterus. Therefore, there is no guarantee that a PGS/PGD embryo will give you a life birth.

If you and your partner are interested in or have any concerns about PGD and PGS, be sure to speak to your fertility specialist to address concerns, inquiries and options.