PGT and Embryo Genetic Testing: What to Understand Before You Decide

What PGT actually is

Preimplantation genetic testing, usually shortened to PGT, is an optional lab step some patients add to an IVF cycle. Once embryos have developed in the lab and reached the blastocyst stage, an embryologist removes a small number of cells from the outer layer of each embryo and sends them to a genetics lab. The embryos are frozen while the results come back, and only embryos that pass are considered for a later transfer.

The goal is to learn something about an embryo before it goes into the uterus, rather than after a transfer has already succeeded or failed. That sounds straightforward, but PGT is not one test. There are a few versions, and they answer very different questions. Knowing which one a fertility clinic is talking about is the first thing to get clear on.

The three main types

PGT-A: counting chromosomes

PGT-A checks whether an embryo has the expected number of chromosomes. When the count is off, the medical term is aneuploidy, and it is one of the more common reasons a transfer does not implant or a pregnancy ends early. Aneuploidy also becomes more likely as a person ages. Clinics use PGT-A to try to pick an embryo with a normal count, hoping to shorten the path to a pregnancy and reduce the odds of a loss.

PGT-M: a known inherited condition

PGT-M is for couples who carry a specific single-gene condition that runs in the family, such as cystic fibrosis or sickle cell disease. If both partners are carriers, or one partner has a dominant condition, PGT-M can identify which embryos inherited it. This usually involves building a custom test for that family before the cycle, so it takes planning and a conversation with a genetic counselor well in advance.

PGT-SR: structural rearrangements

PGT-SR is used when a parent has a known chromosomal rearrangement, such as a translocation, where pieces of chromosomes are arranged in an unusual way. Someone can be healthy themselves but still produce embryos with missing or extra genetic material. PGT-SR looks for embryos with a balanced arrangement.

Who tends to consider it

PGT is not automatic, and plenty of successful IVF cycles skip it entirely. Patients who raise it with their doctor often fall into a few situations: a history of repeated miscarriage, several transfers that failed to implant, a known genetic condition in the family, or an age where chromosome errors are more common. Some people simply want as much information as possible before a transfer. None of these makes testing mandatory. It is a decision to weigh with your care team, not a box everyone checks.

Where PGT helps and where it falls short

The honest version is that PGT gives you more information, not a guarantee. A normal PGT-A result lowers the chance that a failed transfer or miscarriage was caused by a chromosome problem, which can spare some patients repeated disappointment. For a family carrying a serious inherited condition, PGT-M can be the difference between a hopeful transfer and an anxious wait.

What it cannot do is promise a healthy baby. An embryo that passes PGT-A can still fail to implant for reasons the test does not measure, and no genetic screen checks for every possible condition. The testing looks at the questions it was designed for and nothing beyond them.

There is also the matter of mosaic results. Sometimes the sampled cells show a mix of normal and abnormal cells, and the result lands in a gray zone rather than a clean pass or fail. Guidance on what to do with mosaic embryos has shifted over the years, and some of them have gone on to become healthy pregnancies. This is exactly the kind of nuance a genetic counselor exists to walk you through.

The tradeoffs worth talking through

Before adding PGT, it helps to understand what you are signing up for.

• The biopsy itself. Removing cells is a delicate procedure. Done in an experienced lab it is considered low risk, but it is still a step performed on your embryos, and lab quality matters.
• You will be doing a frozen transfer. Because embryos are frozen while results come back, PGT rules out a fresh transfer in that cycle. If a fresh transfer was your plan, this changes the timeline.
• Cost. PGT is usually an add-on charge on top of the IVF cycle, and insurance coverage varies widely. Ask the clinic for an itemized quote rather than assuming it is bundled in.
• Fewer embryos to transfer. Testing can rule some embryos out. For a patient with only one or two embryos, that raises a hard question: test and risk being left with none to transfer, or transfer untested and see what happens.
• Ambiguous answers. Mosaic and inconclusive results are a real possibility, and they can make the decision harder rather than easier.

Questions to bring to your clinic

A few questions tend to cut through the marketing and get you a real answer:

• Which type of PGT are you recommending for me, and why this one?
• Given my age and my number of embryos, do you expect testing to help or could it leave me with fewer options?
• What is your lab's experience with embryo biopsy, and where is the genetic testing done?
• How do you handle mosaic or inconclusive results, and will I speak with a genetic counselor?
• What does this add to my total cost, and what does my insurance cover?

The bottom line

PGT can be a genuinely useful tool for the right patient, and an unnecessary expense for another. The value depends on your history, your age, how many embryos you have, and what you would actually do with the results. Bring the topic up early, ask a reproductive endocrinologist to explain the reasoning for your specific case, and lean on a genetic counselor when the answers get complicated. The best choice is the one made with clear eyes about what the testing can and cannot answer for you.