PGT testing
Registered nurse and expert in reproductive medicine
What is PGT? What’s the difference between PGT-A and PGT-M?
Pre-implantation genetic testing (PGT) is a procedure done in an embryology laboratory where a few cells of an embryo are biopsied (removed) and sent for testing. Depending on your clinic, the testing is either done in their in-house lab or sent to a third party lab. The goal of PGT is to identify embryos with chromosomal abnormalities and/or certain genetic conditions to greatly reduce the risk of miscarriage and increase the chances of a healthy live birth.
PGT-A, or “pre-implantation genetic testing for aneuploidy,” screens an embryo for chromosomal abnormalities. Healthy embryos have 23 pairs of chromosomes, or 46 individual chromosomes, which include the sex chromosomes X and Y that predict gender. After fertilization, in the early stages of cell division inside the embryo, chromosomes can get mixed up, leading to an addition or deletion of its chromosomes, called aneuploidy (pronounced “ann-yuh-ploy-dee”). Examples include 45X (Turner Syndrome) which is a deletion of the X chromosome, and 46XY + 21 (Down Syndrome), which is an extra copy of chromosome 21.
PGT-M, or “pre-implantation genetic testing for monogenic disorders,” screens embryos for a specific genetic mutation that can be passed down by one or both parents. It’s used to help doctors identify and prioritize embryos that don’t carry the inheritable condition. PGT-M is recommended for people who are carriers of illnesses such as Sickle Cell Anemia, Fragile X, SMA (spinal muscular atrophy), and Cystic Fibrosis. Many OBGYNs and fertility clinics offer a blood test called “genetic carrier screening” to determine if the parents carry any diseases that could be passed to their offspring. If the results come back positive and you (and/or your partner, if you have one) are a carrier for an inheritable illness, the clinic will recommend genetic counseling so that you can understand the potential risk of the embryo being affected by the disorder.
There’s a third type of PGT testing called PGT-SR, or “pre-implantation genetic testing for chromosomal structural rearrangement.” This type of testing is done when it is determined that there is a known rearrangement of chromosomes, determined through karyotype testing (a blood test to analyze chromosomes under a microscope). Karyotype testing is recommended when a patient suffers miscarriages. The findings of this testing is highly specialized, locating tiny “micro” deletions, additions and rearrangements on chromosomes that would not otherwise be detected by PGT-A screening.
What’s the goal of PGT testing?
PGT helps screen for genetic abnormalities in an effort to reduce the risk of miscarriage (PGT-A) or passing down inheritable traits (PGT-M). It helps you and your doctor understand which embryos are genetically normal and more likely to result in a healthy pregnancy to term.2 As an added bonus, the test results can reveal the sex of each embryo (quick tip: tell your doctor ahead of time if you want it to be a surprise!).
The bottom line
PGT testing of embryos is a great treatment option to rule out chromosomal or inheritable genetic conditions in your offspring. Your doctor will do a complete history intake and physical exam that will help you determine if PGT testing is right for you.
What’s the PGT testing process?
It all happens behind the scenes. After eggs are retrieved in an IVF cycle and fertilized with sperm in the embryology lab, the embryos will be watched closely as they grow in the lab. Embryos start as simple 2-cell structures, and divide rapidly over the course of about 5–6 days into hundreds of cells. At this stage, called the “blastocyst” stage, an embryologist will take a biopsy, or remove a small number of cells, from each embryo and send them to a lab for testing. The embryos will be frozen right after the biopsy is performed in order to stop the growth, while your doctor awaits the PGT results — generally, it takes about two weeks. Once you know the details about the embryos’ genetic makeup, you and your doctor can decide on next steps, whether that’s moving on to a transfer cycle, repeating an IVF cycle, or keeping the embryos in storage for future use.
The bottom line
Some people decide to test the embryos because they’re already doing IVF and it’s just one extra lab procedure, while others are reluctant to handle the embryos more than necessary. Aside from being a medical indication, the choice to PGT test can come down to a personal decision.
What happens if the embryos come back as genetically abnormal? What are my options?
Before you start an IVF cycle with PGT testing, you’ll have to fill out consent forms, including an “embryo disposition form,” which lays out your decisions about embryos in certain situations, such as divorce and death. There will also be a section asking your preference in the case that embryo biopsy results come back abnormal. Most clinics only offer two options: discard the embryos or donate them to research. Be sure you understand your options and feel comfortable in making a selection.
Some clinics will store abnormal embryos for you or allow you to transfer them to another clinic, if you don’t want to discard or donate them for personal or religious reasons. It’s important to have a clear understanding of your options before you begin your cycle.
How do genetic abnormalities happen in the first place?
Age, environmental factors, and nature are some causes for genetic abnormalities. It’s very difficult to pinpoint exact causes, but we do know that age of the egg and sperm impact aneuploidy rates.
What are some of the controversies around PGT testing?
Ethics: Some people believe that being able to test for genetic disorders and discard impacted embryos is ethically murky. Others don’t believe it’s right to be able to select an embryo based on sex. Because the technology is evolving so quickly, it can become a slippery slope!
Accuracy: PGT testing is scientifically sound, but it’s not perfect.3 Some — not all! — genetic abnormalities documented in PGT-A will self-correct over time in the womb as cells divide and reproduce, so even if there’s an abnormality reported, it may not be a problem. Your doctor will tell you more about your specific situation and help you understand which embryo(s) to transfer first.
Cost: PGT testing is still expensive and it’s typically not covered by insurance, which can make it inaccessible for some people.
Usefulness: While PGT-A is a great treatment option to help people select and prioritize the best quality embryos, it isn’t always the best choice for people who have a low embryo yield (think one or two). The first hurdle in the PGT process is the embryos growing well in a lab until they reach the criteria for biopsy (by day 5, 6, and even day 7). It’s common for embryos not to grow well in a lab, so those that don’t progress well enough won’t be eligible to be tested. The age of the egg and the quality of the lab are big indicators of success.
In cases where the embryos’ growth slows down by day 3, your doctor may suggest doing a transfer and forgo pushing the embryos to day 5 because the risk of having nothing to biopsy is too high, and more often than not, abnormal embryos do not result in pregnancy. You and your doctor will discuss risks and benefits together.
How much does PGT testing cost?
It depends on the lab doing the testing and your clinic’s contract with that facility, if testing isn’t done “in house”. Some clinics charge a flat rate to test, say, up to 5 embryos, while others charge for each embryo tested.
In general, you can expect to pay about $3950 to biopsy and test up to 4 embryos. That cost increases with each additional embryo.
Is PGT testing safe?
Yes. There’s a very low risk of damaging the embryo during the biopsy process.
Is PGT testing suitable for me?
This is a great question, and many factors go into the decision. PGT testing started as a means to eliminate inherited genetic conditions and to help determine an embryo’s “health” status prior to implantation. Before PGT, these tests were only possible during pregnancy, so the thought process is “why wait until the end of the first trimester if we can know ahead of time?” But it’s not that simple.
Embryos don’t always survive in the lab. Manipulating embryos could be more detrimental than letting nature take its course. It’s an ethical and religious dilemma for many. However, PGT testing is a safe lab procedure that is recommended by doctors in cases of advanced maternal age (35+), recurrent pregnancy loss, and when there is a known inheritable condition.
PGT-M testing is recommended if either partner is a carrier for an inheritable illness.
PGT-SR testing is recommended for people who have had multiple miscarriages and have done testing that shows they have a specific chromosomal rearrangement that is detectable with testing.
Who shouldn’t consider PGT testing?
Depending on the fertility clinic where you are seeking treatment, it may not be recommended to test your embryos if you are under the age of 35 and have no known genetic factors that may increase your risk of miscarriage.
If you’re considering a fresh embryo transfer, PGT testing isn’t an option.
Still have questions about PGT testing?
“I would always suggest writing down your questions before an appointment, and join a support group to engage with others who understand what it’s like to go through fertility treatment.”
Ogechi
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