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Pre-Implantation Genetic Testing (PGT) 101

 


 

What is Preimplantation Genetic Testing (PGT)?

 

Preimplantation Genetic Testing (PGT) refers to the screening tests that can be performed on an embryo as part of in vitro fertilization (IVF) process. PGT is conducted by extracting one or more cells from the embryo that is growing in the IVF laboratory. The PGT test will then proceed to analyze the DNA of the embryo in order to detect any genetic defects that can cause problems during pregnancy and/or to the unborn child's health later on in life. The testing will take place prior to the process of transferring the embryo into the uterus.

 


 

Why do You Need PGT?

 

Preimplantation Genetic Testing (PGT) is mainly developed with the purpose of increasing the chance of having a successful pregnancy through IVF treatment. Additionally, PGT results enable the embryologist to select the embryo with the highest chance of survival, therefore reducing the chance of miscarriage as well as avoiding the trauma of having to terminate a pregnancy. Besides that, another advantage of undergoing PGT would be to ensure your unborn baby does not carry genetic defects that can lead to death or inherited genetic conditions that could cause severe health problems in the future. 

 


 

Types of PGT

 

There are several types of PGT that can be carried out to examine the embryo for genetic errors. Bear in mind that not all types of PGT are offered in every fertility clinic due to the need for different specialist personnel and specific pieces of equipment in order to carry out the tests. However, there are three types of preimplantation genetic tests (PGT) that are commonly available at most fertility clinics, namely: 

  1. Preimplantation genetic testing for aneuploidies (PGT-A)
  2. Preimplantation genetic testing for monogenic (PGT-M)
  3. Preimplantation genetic testing for structural rearrangement (PGT-SR)
All three PGT mentioned above aim to analyze for a specific type of genetic disorders and are performed independently. Accordingly, you may not need to take all the tests but only a specific one that addresses your current condition.

 


 

Preimplantation Genetic Testing for Aneuploidies

(PGT-A)

 

PGT-A is a genetic test that aims to examine for chromosomal abnormalities in the embryos. Aneuploidy refers to the condition of embryos with extra or missing chromosomes. Embryo with chromosomal abnormalities is found to be the most common cause of IVF treatment failure during the implantation stage. Even if the implantation is successful, the baby will be born at risk of having a genetic condition like Down syndrome which is the most common genetic condition resulting from chromosome disorders. PGT-A result helps to ensure that only embryos without chromosomal abnormalities are selected for implantation.

PGT-A is an appropriate test for the majority of IVF patients and is highly recommended for:

  1. Women over the age of 35,
  2. Women who have had experience with multiple miscarriages
  3. Women who have had prior pregnancies with chromosomal abnormalities
  4. Women who have had multiple unsuccessful IVF cycles
  5. Couples with severe male factor infertility

 


 

Preimplantation Genetic Testing for Monogenic

(PGT-M)

 

PGT-M enables the parents to reduce the risk of having children with known inherited disorders caused by genetic mutations. This is a sophisticated genetic test designed to analyse the embryo for specific gene mutations that one or both parents are known to carry and/or at a high risk of passing it down to their children. PGT-M is able to test for large numbers of single gene disorders including common single gene disorders conditions such as  Thalassemia, sickle cell disease, spinal muscular atrophy and cystic fibrosis. 

Monogenic or single gene disorders are inherited gene mutation conditions, therefore genetic reports from other members of your family may be required to ensure a more accurate result. PGT-M result allows the embryologist to ensure that only embryos with no genetic mutation are transferred for implantation.

PGT- M is highly recommended when:

  1. You already have a child with serious genetic conditions.
  2. You have previously had pregnancy termination due to serious genetic conditions.
  3. You have a family history of genetic problems or chromosome problems.
  4. Both parents are known to carry specific genetic disorders.

 


 

Preimplantation Genetic Testing for Structural Management

(PGT-SR)

 

PGT-SR is the genetic test conducted on the embryo with the aim to screen for structural chromosomal rearrangements. Parents with known chromosomal rearrangements are at more risk of producing embryos with unbalanced chromosomal rearrangements. This test is for parents with known chromosomal rearrangement genetic conditions. 

Chromosome rearrangements refer to any changes to the size or arrangements of the chromosomes. Different types of chromosomal rearrangement can include:

  1. Deletions —in which a  segment of the chromosome is missing
  2. Duplications — in which there is an extra segment of chromosome 
  3. Inversion – wherein a segment of a chromosome has been inserted into the incorrect location
  4. Translocation – when two segments of chromosomes break off and swap places

Parents who carry the above mentioned rearrangements are known as balanced translocations or inversion carriers. The carriers have all the correct information in their chromosomes aside from some of the genetic material found in different locations than expected. The carriers are also generally healthy but have a higher risk of miscarriages, fertility problems, stillbirths or having children with genetic abnormalities.

PGT-SR can identify the embryo with the correct amount of genetic material (referred to as balanced or normal). The embryologist can further distinguish between balanced and normal embryos which allow for embryos without any chromosomal rearrangement carrier to be transferred for implantation. This way the parent can prevent the next generations from having the risk of chromosomal rearrangements.

 


 

Legal and Ethical Considerations Surrounding PGT

 

Since the first time PGT (formerly known as Preimplantation Genetic Diagnosis, PGD) is introduced, there have been resounding voices of concern over the legality and moral aspect of undergoing the tests. In Malaysia, PGT is legal and permissible by both civil and Sharia law. Islam commands to seek or take up treatment when one is inflicted with illness or disease. Thus, the usage of PGT is in line with the command as PGT enables the parents to seek for a cure, treatment and prevention of chronic genetic illness.

 


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