PGT Testing
Welcome to our guide to PGT testing: digestible, comprehensive and reviewed by medical experts. Whether you’re brand new to fertility treatment or a pro already, this guide is for you to better understand the ins and outs of pre-implantation genetic testing.
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.
“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
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.
