If you are currently planning to start in vitro fertilization (IVF), you may feel overwhelmed by the decisions you have to make. Your physician and you (and perhaps a partner) will discuss IVF protocols, the fertilization method, and what to do with any surplus embryos. Another important decision you’ll need to make is whether to do preimplantation genetic testing (PGT).
PGT is a procedure that spot screens for abnormalities in embryos to help identify the best embryo to transfer and hopefully decrease the risk of an unsuccessful transfer. In addition, it can be used to screen for genetic diseases in patients who are at risk of transmitting a genetic disease (like BRCA, a breast cancer gene) to a child.
PGT includes three genetic screening tests for embryos. They are usually referred to by their acronyms. Here’s what you need to know about PGT to decide if it’s the right choice for your fertility journey.
What Is PGT?
PGT is an umbrella term covering three main subsets of genetic testing. They include preimplantation genetic testing for aneuploidy (PGT-A), preimplantation genetic testing for monogenetic/single-gene diseases (PGT-M), and preimplantation genetic testing for structural chromosomal rearrangements (PGT-SR). PGT-A is the most common genetic test for those going through fertility treatments like IVF.
By understanding what each of these tests does, you can speak to your fertility specialist and see if they might be right for you.
PGT-A screens for chromosome abnormalities in embryos. It counts the 46 chromosomes in an embryo and detects whether there is an extra or missing chromosome – this is clinically referred to as aneuploidy. This can reduce the risk of implanting an embryo with a genetic condition such as Down syndrome (where there is an extra chromosome), and it can help predict which embryos will implant most successfully during IVF, resulting in pregnancy.
Formerly known as preimplantation genetic diagnosis (PGD), PGT-M (monogenic/single gene defect) is a screening tool used for couples who may be at an increased risk of having a child with a specific single gene disorder. Those who may benefit from PGT-M include couples who are carriers of the same autosomal recessive condition, such as Cystic fibrosis.
When patients (and their partners) know this information before IVF, they are encouraged to undergo screening for recessive conditions. For these conditions, if an embryo inherits one mutated gene copy from each parent, the child would be affected by the disease. PGT-M can detect mutations from parents with inherited genetic diseases, such as Huntington’s disease, or a genetic cancer risk like the BRCA gene.
PGT-SR is performed when a patient (or their partner) is known to have a chromosomal rearrangement – pieces of chromosomes are missing, duplicated, or rearranged. Individuals with chromosomal rearrangements may experience recurrent pregnancy loss or have a child affected by a chromosomal rearrangement. Many times these patients are healthy and would otherwise not show any signs or symptoms.
Patients with recurrent pregnancy loss (two or more clinical pregnancy losses) should have a karyotype to screen for a chromosomal rearrangement prior to starting IVF. By detecting the chromosomal rearrangement in an embryo, PGT-SR can reduce the risk of having a child affected by a chromosomal abnormality and the risk of another pregnancy loss.
By working closely with a fertility specialist who understands your fertility process and health history, they’ll be able to confidently recommend whether a specialized test like PGT-SR can help in addition to a more commonly used screening tool like PGT-A.
The Pros and Cons of PGT-A
Here are some factors to remember as you discuss PGT-A with your partner and fertility specialist.
Pro: Optimal Embryo Selection
One of the main goals of PGT-A is to ensure that your IVF is successful. By screening the embryos before implantation, the doctor is able to identify the embryos with a higher chance of a successful pregnancy. Since pregnancy rates are higher with embryos that have undergone PGT-A, only one embryo is transferred. Single embryo transfer is preferred since pregnancy complications increase in pregnant patients with more than one fetus.
Pro: Sex Selection
PGT-A screens all 46 chromosomes, which means information on embryo sex is also available. Some patients prefer not to know the sex of the embryos. Others may be interested for the purpose of family balancing or for rare situations in which a genetic disease is inherited based on embryo sex.
Pro: Reduce Stressful Decisions
The most common cause of pregnancy loss is a chromosomal abnormality in the developing fetus. Some chromosomal abnormalities can increase the risk of stillbirth, shorten lifespan, or cause significant medical problems. By screening embryos for chromosomal abnormalities, some of these tragic situations can be avoided. By screening embryos with PGT-A, hopefully, the risk of miscarriage will decrease, and the number of embryo transfer cycles needed to become pregnant will also decrease.
Con: Extra Cost
IVF is expensive, and additional testing like PGT-A can add cost. Your insurance also may not cover PGT-A with your fertility treatment. However, it’s worth noting that with PGT-A, you may not need multiple embryo transfer cycles to conceive, helping to negate that cost. Together with your fertility specialist, you can discuss the expense of both IVF and PGT-A to your options and how much extra testing may cost.
Con: Embryo Damage
All genetic screening tests require embryologists to remove cells (usually five-seven) from the trophectoderm – which are the cells that become the placenta. This testing is usually performed on a day five embryo (blastocyst) when the embryo is less likely to be impacted by removing a small number of cells. Cells from the inner cell mass are not disturbed as these cells will develop into the fetus. In labs that are routinely performing PGT-A, the risk of damage to the embryo is very low because of the expertise and experience of the embryologists. Your fertility specialist will help you decide if this testing is the best choice for you and will also discuss the genetic screening options that are available after you conceive.
Con: False Results
Just like with any type of testing, there is a chance that a PGT-A test can deliver a false negative or positive, meaning that healthy embryos may go unused when they could have been transferred, or an embryo with a chromosomal abnormality is transferred based on test results.
This test is also not a diagnostic test but a screening test. This is because the biopsied cells come from the cells that become the placenta and not the cells that become the fetus. This is not unique to embryo testing as early genetic screening in pregnancy – such as noninvasive pregnancy testing (NIPT), which is offered at 10-12 weeks is also screening the DNA from the placenta. The earliest testing that can be done on the DNA of the fetus is at 15 weeks of pregnancy via an amniocentesis.
In addition, sometimes embryos contain 2 different cell lines – these are called mosaic embryos. Mosaic embryos can implant and result in a live birth but do so at a lower rate than chromosomally-normal embryos. Mosaic embryo results require individualized counseling between the physician and patient before making the decision to transfer.
Talk to your fertility specialist about the risk of a false PGT-A result so that you can factor this into your decision-making process.
Is PGT-A the Right Choice for Me?
Many personal factors come into play when deciding to do PGT-A testing on your embryos. This includes:
- Age: Women who are older who are undergoing IVF to create embryos have an increased risk of chromosomal abnormalities in those embryos. Therefore, women 35 years or older may want to use PGT-A to select the embryo that has the highest chance of pregnancy.
- Health history: If you’ve had a history of recurrent miscarriages, unsuccessful embryo transfer cycles, or have had abnormal genetic testing results in the past, PGT-A may offer you peace of mind before an IVF transfer.
- The number of embryos: It is important to note that not every fertilized egg will develop into a blastocyst (day five embryo). There is a risk that no embryos develop to day five or that no embryos are chromosomally normal. Thus, some patients who proceed with PGT-A may not have a viable embryo to transfer.
- Time: After the embryos are biopsied on day five, the embryos are cryopreserved until embryo transfer. The results from the genetic testing of the embryo may take as long as two weeks. Therefore, patients who test the embryo will usually transfer the embryo the next month. Studies have also shown that for some patients, a frozen embryo transfer has a higher live birth rate than a fresh transfer.
This is just a glimpse of the considerations when thinking about PGT-A testing. To make the best-informed decision, consult with a fertility specialist regarding your situation. They will be able to go over your health history and fertility journey and answer any questions you may have to help you confidently reach your decision.
At RGI, we offer an IVF 100% Success Guarantee Plan to qualifying patients because we’re confident in our experience and technology to help you get the family of your dreams. For some patients, an important part of that will include PGT-A testing. Schedule a consultation with a fertility specialist today and learn more about your fertility and the available treatment options.