Preimplantation Genetic Testing

Preimplantation genetic testing (PGT), formerly referred to as preimplantation genetic diagnosis (PGD), is the process of screening embryos for a given genetic mutation or condition. The goal of PGT is to reduce the chance of having a child affected by a known mutation that causes a genetic disease. This is done together with in-vitro fertilization (IVF). Embryos are screened in a laboratory for a genetic condition before they are transferred.

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PGT FAQs

PGT-M = PGT for monogenic disorders 

This type of PGT is used to screen embryos for a mutation that causes a monogenic disorder. A monogenic disorder is a genetic condition that is attributed to a mutation in a gene. This includes both autosomal dominant conditions, which are caused by one gene mutation, like BRCA1 or BRCA2, and autosomal recessive conditions, which are caused by two gene mutations, such as cystic fibrosis.

 

PGT-A = PGT for aneuploidy

This type of PGT is used to screen embryos for different chromosome abnormalities, or aneuploidies. Aneuploidy is defined as the presence of extra or missing chromosomes. A common aneuploidy is trisomy 21, or Down’s syndrome. An individual with Down’s syndrome has three copies of chromosome 21, instead of the expected two. PGT-A screens embryos for different aneuploidies, including Down’s syndrome, to see if there are any extra or missing chromosomes or even extra or missing pieces of a chromosome, that may cause an increased risk for failed embryo transfer, miscarriage, or an affected child.

 

PGT-SR = PGT for structural rearrangements

This type of PGT screens embryos to see if they have inherited the same rearranged chromosome as their affected parent. Sometimes an individual has all 46 of their chromosomes, but one is abnormally structured. This is unlikely to cause any health issues for the individual themselves but can become problematic, however, when they attempt to have children. This is often identified with specific genetic testing. These individuals are at an increased risk to have reproduction and fertility issues, such as recurrent miscarriage and stillbirth, due to passing on a chromosome that has extra or missing genetic material. 

 

All types of PGT (M, A, and SR) are completed in the same manner and done together with IVF. After the egg retrieval, the sperm and egg will be combined to form an embryo, which starts to develop. Around Day 5, the embryo is a mass of cells that resembles a ball that is composed of two parts: an outer layer and an inner layer. At this point, an embryo biopsy is performed, which involves removing a couple of cells from the outer layer of the embryo, which will eventually develop into pregnancy structures, like the placenta and membranes. These cells are generally expected to be representative of the entire embryo.

The embryo will stay in your reproductive center while the biopsy is sent to the laboratory of your choice for further testing. The laboratory will design a custom test for the embryos, called a probe, based on your personal and family medical history. This may require meeting with a reproductive specialist, genetic counselor, or laboratory technician to determine and coordinate any additional documentation or blood/saliva samples needed for test design.  Blood/saliva samples will be needed from the parents of the embryo, and often from other family members as well. The probe can take a few months to complete.

The number of cells being tested is much smaller with PGT-M than when you have genetic testing done on a vial of blood or saliva. The embryo biopsy is microscopic.

The cells that are tested are destroyed in the process of testing. The biopsied cells from the embryos are not returned. If the egg or sperm were tested, they would not be able to be used.

Most laboratories that perform PGT on embryos quote an accuracy rate of over 99%. This means that over 99% of the time, the laboratory will be able to accurately predict that an embryo will have a genetic or chromosome condition.
PGT is a screening test, not a diagnostic test. This means that the information collected is highly accurate, but requires further testing to confirm the reported results. This can be done during pregnancy, with amniocentesis or chorionic villus sampling (CVS), or after birth.

The cost of PGT varies depending on various factors, including insurance coverage, personal and family medical history, laboratory costs, and more. Including IVF, which is necessary when doing PGT, can be upwards of $50,000 without grants or insurance.
Spending money to pursue IVF and PGT-M is not a guarantee of success in having a child. Multiple cycles may be required to have enough healthy embryos to attain a healthy pregnancy. Miscarriages may happen, usually for unexplained reasons.
If insurance covers, you can try to complete as many procedures as possible in one insurance calendar year. Some women try doing the egg retrieval in the same calendar year as their bilateral mastectomy and reconstruction, to take advantage of going over the out of pocket maximum.

Cost
There are many fertility treatments, including IVF and PGT, that may not be covered by insurance. Additional costs for these processes may be a consideration for patients considering this option, especially since multiple cycles may be needed to obtain the desired results.

Thawed embryos may have a lower success rate
Embryos are required to be frozen prior to testing. Studies have shown that there is a small chance that thawing embryos multiple times may decrease the chances of successful implantation and pregnancy.

Not every embryo makes it past biopsy
Not every embryo makes it past the biopsy stage, due to its fragile state. For example, a patient may have 10 embryos available for testing, but only 4 make it past the biopsy stage and can undergo testing. When this happens, the embryo stops growing and cannot be used for transfer.

PGT does not guarantee healthy embryos.
An individual may find that all the tested embryos have a genetic condition, but none of them are affected by the condition or a combination of both. Multiple cycles may be required until the desired amount of embryos is achieved.

PGT does not guarantee a successful transfer, ongoing pregnancy, or birth.
PGT improves the chances, but does not guarantee, that a patient will have the pregnancy outcome they desire. There is always a 3-5% background risk that a child will be born with another health condition or birth defect, such as autism, that cannot be predicted prior to birth.

Hormones are given to stimulate the development of egg follicles before the retrieval, and again after the implantation of the embryo. Some women report that taking hormones can make them feel like they are on an emotional roller coaster.

Once the pregnancy is well established, you will switch from the fertility practice to your regular obstetrician. This can feel like a big adjustment, since you will no longer have as many visits with the doctor.

  • Individuals who have a mutation associated with hereditary cancer EX: BRCA1, BRCA2
  • Individuals who have a mutation associated with a genetic condition EX: Huntington disease, Marfan’s syndrome
  • Couples who are both mutation carriers for the same recessive genetic condition EX: Cystic fibrosis, Tay-Sachs disease
  • Individuals who have a personal or family history of a genetic disease, including a pregnancy or child with a genetic or chromosome condition.
  • It is important to speak with a fertility or reproductive specialist that can help provide more information and guidance regarding pursuing PGT.

Embryos can be screened for most genetic disorders, based on an individual’s personal and family medical history. It is only able to test for a mutation that has been identified in one of the parents. As amazing as genetic testing technology can be, it is important to remember that PGT does not guarantee a successful pregnancy and a live-born child.

To learn more about PGT, including personalized medical, technical, and financial considerations, please reach out to a reproductive specialist or medical provider near you.

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ADDITIONAL RESOURCES

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