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Everything You Need to Know About Preimplantation Genetic Testing (PGT)

Before you start your IVF cycle, you should decide with your doctor whether you’d like your embryos to undergo Preimplantation Genetic Testing (PGT). But when is this the right choice, and what kind of PGT is best for your concerns?

6 Second Snapshot

  • Preimplantation Genetic Testing (PGT) is an embryo biopsy procedure done in a laboratory that screens for genetic or chromosomal abnormalities.
  • You can choose from several types of PGT depending on your concerns, which may include recurrent miscarriages or a family history of a genetic disorder.
  • Deciding to undergo PGT is a very personal decision. Your care team can help you decide if PGT is the right choice for you.

Embryo grading helps determine which embryo to transfer

After your eggs have been fertilized and have reached a critical stage of growth, an embryologist will use a grading system to determine which embryo to transfer. This process, known as embryo grading, helps embryologists and physicians understand the quality of a patient’s embryos, and decide which ones to prioritize for transfer. This is a standard part of the IVF process.

What is PGT and how is it conducted?

Depending on your concerns, you may choose a more intensive form of testing before deciding which embryo to implant. Here’s where Preimplantation Genetic Testing (PGT) comes in. PGT is an embryo biopsy procedure done in a laboratory that screens for genetic or chromosomal disorders.

There are several types of PGT.

  • PGT-A testing screens embryos to make sure they have the correct number of chromosomes. More or fewer than the correct number of chromosomes can lead to a failure to implant, miscarriage, or a child with genetic conditions. However, recent studies have shown that aneuploid embryos (embryos with an incorrect number of chromosomes) and mosaic embryos (in which there are normal and abnormal cells within a single embryo) can sometimes correct themselves as they grow and result in healthy babies. While this bears more research, it’s encouraging to know that more eggs may be viable than previously thought.
  • PGT-M screens for monogenic (single gene) disorders that could significantly alter quality of life, such as cystic fibrosis, sickle cell anemia, muscular dystrophy, or the BRCA1 or BRCA2 mutation that increases a woman’s chance of developing breast or ovarian cancer. If you or your partner have a family history of a monogenic disorder or are both carriers of an autosomal recessive disorder, PGT-M can check for these single-gene mutations.
  • PGT-P is a relatively new screening test for polygenic (caused by multiple genes) disorders such as diabetes, cancer, and coronary artery disease. However, polygenic disorders are complex with a strong environmental component, and PGT-P does not accurately screen for this complexity. There are also concerns about how ethical PGT-P is, since it can be used to select desired traits as well as reduce disease risk.
  • PGT-SR checks for structural abnormalities in the chromosomes. If you or your partner has a chromosome rearrangement (i.e. balanced translocation), PGT-SR can check for this in the embryo. These abnormalities can increase your chance of miscarriage.

At what stage of the IVF cycle would you do PGT?

After your embryos have been created and have matured for about 5-6 days, they reach a stage called the ‘blastocyst’ stage. At this point, several cells from the wall of the embryo, known as the trophectoderm, can be removed to undergo PGT in a laboratory. Since the trophectoderm layer develops into the placenta and other pregnancy-supporting membranes, the test doesn’t take any cells that would develop into your baby. While those cells are being tested, the embryo is carefully cryogenically frozen. Once the PGT results come in, you and your clinician can select an embryo for implantation. With PGT, you can also learn the gender of the embryos.

How to decide whether to do PGT

There are many factors to weigh when considering PGT. Here are some of them:

  • For patients who have experienced recurrent miscarriages or repeated implantation failure, PGT-A may help. One study showed that PGT-A may increase your chance of a live birth to about the same as a patient without those concerns. For patients older than 36, the live birth rate improved to 54.1% from 32.8%.
  • For patients without these concerns, the drawbacks of PGT-A (cost, occasional false positives and negatives, potential damage to the embryo) can outweigh the benefits.
  • PGT-M can bring tremendous peace of mind if you have serious concerns about genetic disorders or chromosomal abnormalities.
  • PGT is expensive. For example, PGT-A costs around $5,000, and is rarely covered by insurance. For many patients, this becomes a significant percentage of the overall cost of IVF.

Deciding to do PGT is a highly personal and individual decision. If you’re interested in PGT, it’s important to talk to your care team before starting your IVF cycle to determine which PGT test to do, and whether it’s the right choice for you.

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