What is Preimplantation Genetic Testing and Why Do People Use It?

Understanding Inheritance and What Genetic Testing Has to Offer

Biological inheritance or hereditary describes the passing of genetic material from parent to child. It’s easy to see evidence of traits being passed on when examining the characteristics of family members. Traits like hair color, eye color, facial feature shapes, and heights are easy to spot similarities amongst relatives. However, when there’s a genetic change or variant, this can also be passed on which is why some diseases can run in a family.

For those looking to grow their family, they may consider the diseases that run in their family or they may know they carry a certain genetic or chromosomal condition. Those with specific concerns might consider options for building their biological family that can reduce the risk of having a child with the condition.

With fertility treatment and genetic testing, families can be empowered to have children who not only are free from the specific disease in the family but in turn, free the subsequent generations from being at risk for the disease as well. At ORM, our goal is to help our families create healthy babies. In many families’ cases, undergoing in vitro fertilization (IVF) with preimplantation genetic testing (PGT) can greatly increase their chance of having a healthy baby. 

What is Preimplantation Genetic Testing and What Can it Determine?

Embryologist performing preimplantation genetic testing PGT on embryos

PGT which was formerly termed Preimplantation Genetic Diagnosis (PGD) describes the testing of embryos for genetic diseases and chromosomal disorders. There are three types of PGT: all are done by screening cells from the embryo following in-vitro fertilization (IVF) before an embryo is selected for transfer and a pregnancy is established. 

PGT can identify embryos at risk of having a specific genetic or chromosomal condition. Patients choose to do IVF with PGT in order to significantly decrease their chance of having a child with a certain genetic or chromosomal condition.

There are Three Types of Preimplantation Genetic Testing

There are three types of PGT: PGT-A, PGT-M, PGT-SR. Determining which test is right for you depends on the type of issue you’re seeking to identify. 

Most patients who pursue PGT- M and PGT-SR have either sought it out for a specific genetic or chromosomal condition for which their children are known to be at risk, or are undergoing a fertility evaluation when genetic testing revealed that they have an increased risk to have a child with a genetic condition. PGT-A is typically offered as a routine part of fertility care and is not sought out for a specific condition. At ORM, approximately 90% of our patients opt into PGT-A as a part of their fertility treatment plan.

What is PGT-A?

Preimplantation Genetic Testing – Aneuploidy (PGT-A) is the most common embryo screening test that can be performed prior to conception. During PGT-A, embryos created through IVF are biopsied and screened for all 46 chromosomes. The name of the test refers to looking for extra or missing chromosomes (“aneuploidy”). Aneuploidy is common in embryos and can cause failed implantation, miscarriage, or the birth of a child with health problems.

PGT-A helps identify the embryos that are most likely to implant and result in a successful pregnancy and also reduces the chance of having a child with extra or missing chromosomes which could cause disorders such as Down syndrome. PGT-A also identifies the chromosomal sex of the embryo (XX or XY) and this information is available for those who wish to have it.

What is PGT-M?

Preimplantation Genetic Testing for Monogenic disorders (PGT-M) analyzes the DNA of embryos to look for diseases caused by a variant in a specific single gene. PGT-M is available for the vast majority of serious genetic conditions, as long as the particular gene mutation(s) in the family has been identified through DNA testing. Examples include cystic fibrosis, Tay-Sachs disease, an inherited cancer syndrome, or hundreds of other conditions.

The risk of passing on a genetic condition may have been discovered through routine genetic screening, such as carrier screening, or because a person or their close relative already has a known genetic diagnosis.

While transferring an embryo that has tested “normal” by PGT-M is expected to significantly reduce the chance for the future child to develop the genetic disorder in question, it does not entirely eliminate the risk.

Some examples of single-gene conditions for which PGT can be done are:

  • Pediatric conditions such as cystic fibrosis, spinal muscular atrophy, thalassemia, and sickle cell anemia;
  • Metabolic disorders such as Tay-Sachs disease and Fanconi anemia;
  • Hereditary cancer syndromes such as breast/ovarian cancer predisposition (known to be associated with BRCA1 or BRCA2 genes), Lynch syndrome, and hereditary diffuse gastric cancer;
  • …and hundreds of other autosomal recessive, autosomal dominant, and X-linked genetic disorders.

What is PGT-SR?

Preimplantation Genetic Testing for structural chromosome rearrangements (PGT-SR) screens embryos for inherited chromosome changes such as balanced translocations and inversions. PGT-SR reduces the risk of having a pregnancy or child with an unbalanced structural abnormality, which involves extra or missing genetic material and frequently results in pregnancy loss. PGT-SR can help identify the embryos with the correct amount of chromosomal material to be selected for transfer, increasing the chance of a successful pregnancy for carriers of balanced rearrangements. 

How to decide if PGT is right for you?

Person meeting with genetic counselor to discuss genetic testing and risks

Depending on the situation, PGT might be right for your journey to growing your family. It is important to understand the potential benefits, risks, and limitations of these tests. There are many factors to consider including medical, emotional, moral, and financial. For example, patients may consider the likelihood of a having successful pregnancy or the chance of having a healthy child if PGT is not utilized; whether or not effective treatment is or may become available for the condition in question; possible alternatives to PGT; and their own personal relationship to the genetic condition. 

For more information about PGT, please feel free to contact our genetic counseling team.

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