What is Embryo Preimplantation Genetic Testing (PGT)?

What is Embryo Preimplantation Genetic Testing (PGT)?

Building a family through in vitro fertilization (IVF) means you also have the option of examining the genetics of the embryos. This process is called Preimplantation Genetic Testing (PGT) or Preimplantation Diagnosis (PGD), and it is carried out before the transfer of embryos to the uterus of the Intended Mother or surrogate. 

Yes, it’s a complicated topic, but it is very important to consider. Things like genetics and whether your offspring might be at risk of any inherited disorders or other health risks. 

What is PGT / PGD?

Preimplantation genetic testing/diagnosis (PGT/PGD) is a diagnostic test that determines whether an embryo is affected by a genetic disorder passed on from one or both parents. Once embryos are tested, the parents can select the healthiest embryos in order to improve their chances of having a successful pregnancy. 

The test involves removing one or a few cells from the embryo and checking the DNA in a laboratory. This allows doctors to check for genetic problems that can cause the embryo to fail to implant or for the pregnancy to end in miscarriage. PGT can also help reduce the risk of a child being born with severe defects. 

Technology has improved significantly since PGT was first introduced in 1990, and testing can now detect a wide range of genetic conditions.

There are two screening technologies available when using IVF: PGT-M and PGT-A. 

  • PGT-M = preimplantation genetic testing for monogenic disorders. This checks for a specific genetic disease that may have been passed down by one of the parents. 
  • PGT-A = preimplantation genetic testing for aneuploidy. This examines the embryo’s chromosomes to check for conditions such as Down’s Syndrome. It can also identify the gender of an embryo. 

Who should undergo PGT?

Intended Parents undergoing IVF who may wish to opt for preimplantation testing include those who:

  • Are aged 35 or over
  • May be carrying genetic disorders 
  • Have a history of failed pregnancies or IVF procedures
  • Have DNA mutations or a family history of DNA mutations

What tests can PGT cover?

Every year, the range of genetic tests that can be performed increases. PGT can now include tests for various chromosomal abnormalities, including Down’s syndrome, trisomies (an extra chromosome), monosomies (a missing chromosome), and sex chromosomal abnormalities. It also detects single-gene disorders such as cystic fibrosis, sickle cell disease, and many others. 

Why is PGT / PGD helpful?

A significant advantage of these kinds of tests is that they can help to improve the chance of a successful IVF pregnancy. Genetic issues or inherited disorders are some of the main reasons that embryo transfers fail. 

As an Intended Parent, you’re already investing a large sum of money into building a family through reproductive technology. It only makes sense to ensure that the embryos used for transfer are normal, healthy, and have the best chance of a successful pregnancy – and a healthy baby!

Can we choose the gender of our baby?

Yes, it’s possible to check for – and select – a boy or girl embryo. This process is generally called ‘sex selection.’ The results of the PGT will reveal the sex chromosomes of the embryos, which means Intended Parents can choose which gender they wish to transfer to their surrogate. 

There can be many reasons that IPs choose a particular gender over another. For example, it can prevent certain sex-linked traits such as hemophilia, congenital night blindness, Duchenne muscular dystrophy, or Fragile X syndrome. 

In other cases, parents who already have a son/s may want to have a daughter or vice versa. And in still other cases, a mom- or dad-to-be may just long to add a little boy or a little girl to their family.

Are there risks of PGT?

As with any medical procedure, PGT isn’t 100% perfect. 

For a start, PGT doesn’t come with guaranteed accuracy. An incorrect diagnosis is rare, but it can happen in a very small number of cases. It’s possible for a genetic condition to be missed or for a pregnancy to fail. 

For this reason, couples may also wish to undergo further prenatal testing via blood tests, imaging studies, and other genetic testing to assess their baby’s health throughout the pregnancy.

There is also a small risk that PGT can damage the embryo or reduce its implantation potential. This is less likely if the biopsy is carried out at the blastocyst stage.

It’s also important to note that PGT has only been around for a couple of decades, and some risks may not yet be identified.

The take-home message

PGT is not about making ‘designer babies.’ It’s about testing an embryo’s genetic makeup – not altering it. Most importantly, PGT is done to ensure the health of the baby and the success of the pregnancy, which is extremely important for any parent undergoing IVF. 

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