PGT, or preimplantation genetic testing, is a screening technique used during IVF to check embryos for genetic or chromosomal problems before they’re transferred to the uterus. The goal is straightforward: by selecting embryos without certain genetic issues, you can improve the chances of a healthy pregnancy and reduce the risk of miscarriage or passing on an inherited condition. There are three types of PGT, each designed to catch a different category of genetic problem.
The Three Types of PGT
PGT isn’t a single test. It’s a category that includes three distinct screenings, and which one you need depends entirely on what you’re testing for.
PGT-A (aneuploidy) checks whether an embryo has the right number of chromosomes. A healthy human embryo should have 46 chromosomes. Embryos with too many or too few (a condition called aneuploidy) are the most common reason IVF embryos fail to implant or result in early miscarriage. PGT-A is the most widely used form and the one most people are referring to when they simply say “PGT.”
PGT-M (monogenic disorders) looks for a specific inherited disease caused by a single gene. This is used when one or both parents carry a known genetic mutation. The most common conditions tested for include cystic fibrosis and sickle cell disease on the recessive side, and Huntington’s disease, myotonic dystrophy, neurofibromatosis, and hereditary cancer syndromes on the dominant side. PGT-M can technically be used for any single-gene disorder where the responsible gene has been identified, including X-linked conditions like Duchenne muscular dystrophy and even mitochondrial disorders passed through the mother. In rare cases, it’s also used to find embryos that are an HLA match for a sick sibling who needs a stem cell transplant.
PGT-SR (structural rearrangements) screens for chromosomal structural problems like translocations, deletions, duplications, and inversions. This is typically relevant when one parent is known to carry a balanced translocation, a condition where pieces of chromosomes have swapped places. A balanced translocation usually causes no health problems for the carrier but can lead to recurrent miscarriages because the embryos inherit an unbalanced version.
How the Biopsy Works
PGT requires removing a few cells from each embryo so those cells can be analyzed in a genetics lab. This biopsy happens on day five or six of embryo development, when the embryo has reached the blastocyst stage and contains roughly 100 to 200 cells. At this point, the embryo has two distinct parts: the inner cell mass (which becomes the baby) and the trophectoderm (which becomes the placenta). The biopsy targets only the trophectoderm, leaving the inner cell mass untouched.
The embryologist removes about 5 to 10 cells using either a laser-assisted technique or a direct suction method. The entire procedure needs to happen within about three minutes to minimize stress on the embryo. Fewer laser pulses are preferred because excessive laser use has been linked to a higher chance of misleading results.
After the biopsy, embryos are almost always frozen through a rapid-freezing process called vitrification, typically within 30 minutes. The cell samples are sent to a genetics laboratory for analysis. Once results come back, usually within one to two weeks, you and your doctor can decide which embryos to transfer in a subsequent frozen embryo transfer cycle.
Who Is PGT Recommended For
The recommendations differ by type. PGT-M is clearly indicated when parents are known carriers of a specific genetic condition or have a family history of one. PGT-SR is appropriate when one partner carries a balanced chromosomal rearrangement, which is sometimes discovered after recurrent pregnancy losses.
PGT-A is where the picture gets more nuanced. It’s most clearly supported for older patients who want to transfer a single embryo at a time, since the rate of chromosomally abnormal embryos rises sharply with age. Beyond that, PGT-A is frequently offered for recurrent IVF implantation failure, recurrent miscarriage, and advanced maternal age more broadly. However, major reproductive medicine organizations consider some of these indications “unproven,” meaning the evidence that PGT-A improves cumulative outcomes in these groups is still mixed.
What the Success Rate Data Shows
PGT-A’s impact on success rates depends on how you measure it. Per transfer, embryos that have been screened and found chromosomally normal have a clear advantage. One large study found live birth rates of about 50% per transfer with PGT-A compared to 36 to 39% without it. That’s a meaningful difference if you’re looking at each individual transfer cycle.
But per egg retrieval, meaning when you account for all the embryos created in a single IVF cycle, the gap narrows considerably. The same study found live birth rates of 63.7% with PGT-A versus 52.3% without it per retrieval, a difference that was not statistically significant. The reason: some embryos labeled abnormal by PGT-A might have self-corrected or been viable, so discarding them can offset the per-transfer advantage. This is an important distinction because it means PGT-A helps you get pregnant faster by avoiding failed transfers, but it may not dramatically change your overall chance of having a baby from a given egg retrieval.
Miscarriage Reduction
Where PGT-A shows its clearest benefit is in reducing early pregnancy loss. An analysis of over 133,000 IVF cycles reported to the national registry found the early miscarriage rate was 7% with PGT-A compared to 12.5% without it. The benefit was most dramatic for older patients. Women over 42 had a miscarriage rate of just 3.4% with PGT-A versus 12.6% without it. For women 38 to 40, it was 6.4% versus 15.6%. Even for women under 35, there was a modest reduction from 11.3% to 8.1%.
Understanding Mosaic Results
Not every PGT-A result comes back as a clean “normal” or “abnormal.” Some embryos receive a mosaic result, meaning the test detected a mix of normal and abnormal cells. This doesn’t necessarily mean the embryo itself is mosaic. Because the test analyzes DNA from a small group of cells collectively rather than examining each cell individually, the result is an estimate. A mosaic-labeled embryo could actually be fully normal, fully abnormal, or truly a mix.
Research has found that embryos with lower levels of predicted mosaicism (under 50%) may develop just as well as fully normal embryos, showing no difference in ongoing pregnancy or miscarriage rates in at least one prospective study. The reproductive medicine community has gradually become more open to transferring embryos with mosaic results, particularly when no fully normal embryos are available. However, long-term data on children born from mosaic embryo transfers is still limited, as studies so far have only tracked outcomes through the newborn period.
Limitations and What Can Go Wrong
PGT is not a guarantee. Several limitations are worth understanding before you decide.
- Diagnostic failure: For PGT-M specifically, about 10 to 12% of biopsied embryos produce inconclusive results, meaning the test couldn’t give a clear answer. A second biopsy may be needed.
- False results: Because the biopsy samples the outer layer of the embryo rather than the part that becomes the baby, there’s a small chance the genetics of those cells don’t perfectly represent the embryo as a whole. An embryo labeled abnormal might actually be healthy, and vice versa.
- Fewer embryos to work with: After testing, some embryos will be classified as abnormal and typically won’t be transferred. If you started with only a few embryos, you could end up with none that pass screening.
- No test for everything: PGT-A checks chromosome number, PGT-M checks for one specific gene, and PGT-SR checks for structural rearrangements. None of them screen for every possible genetic condition, birth defect, or developmental issue.
Cost of PGT
PGT adds a significant expense on top of a standard IVF cycle, and the bill typically comes in two parts: the embryo biopsy fee charged by your fertility clinic, and a separate genetics laboratory fee for the actual analysis. Nationally, PGT-A adds roughly $4,000 to $5,000 for the biopsy and lab work combined. On top of that, because embryos are frozen during testing, you’ll also need a frozen embryo transfer cycle, which adds another $4,000 to $5,000 at many clinics. The total additional cost for PGT-A is often $8,000 to $10,000 beyond your base IVF cycle, though some clinics offer significantly lower pricing. PGT-M and PGT-SR can cost more because of the custom test design required for your specific genetic situation. Insurance coverage for PGT varies widely, so it’s worth checking your plan before committing.