PGT stands for preimplantation genetic testing, a group of lab techniques used during IVF to check embryos for genetic or chromosomal problems before they’re transferred to the uterus. There are three types, each screening for something different: PGT-A (aneuploidy), PGT-M (monogenic disorders), and PGT-SR (structural rearrangements). If you’ve seen this abbreviation on a fertility clinic’s website or in your treatment plan, here’s what each one means and how they differ.
The Three Types of PGT
PGT-A screens for aneuploidy, which means an embryo has too many or too few chromosomes. Humans normally have 46 chromosomes, and having the wrong number is the most common reason embryos fail to implant or end in early miscarriage. PGT-A is the most widely used form and the one most people encounter during a standard IVF cycle.
PGT-M tests for monogenic disorders, meaning a specific single-gene condition that runs in a family. This is the test used when one or both parents are known carriers of conditions like cystic fibrosis, sickle cell disease, or Huntington’s disease. The lab looks for that exact genetic mutation in each embryo.
PGT-SR checks for structural rearrangements in the chromosomes. Rather than counting chromosomes, it looks at whether segments have been deleted, duplicated, or flipped. This type is typically recommended when a parent carries a known chromosomal rearrangement, such as a translocation, that could lead to miscarriage or developmental problems.
Why the Name Changed From PGD and PGS
If you’ve come across older articles or forum posts, you may have seen the terms PGD (preimplantation genetic diagnosis) and PGS (preimplantation genetic screening). These were replaced when the International Glossary on Infertility and Fertility Care updated its terminology. What was called PGD is now PGT-M, and what was called PGS is now PGT-A or PGT-SR. The umbrella term PGT was adopted to make it clearer that these are all variations of the same basic process, just looking for different things. You’ll still see PGD and PGS used informally, but PGT is the current standard.
How the Testing Works
All three types of PGT follow the same basic process. After eggs are fertilized through IVF, embryos grow in the lab for five or six days until they reach the blastocyst stage, a ball of roughly 100 to 200 cells. An embryologist then removes a few cells from the outer layer (the part that becomes the placenta, not the part that becomes the baby). Those cells are sent to a genetics lab for analysis, and the embryos are frozen while you wait for results.
Results typically come back within one to two weeks. Each embryo gets a report: normal (euploid), abnormal (aneuploid), or in some cases, mosaic, meaning a mix of normal and abnormal cells were found in the sample. Only embryos with favorable results are considered for transfer.
What Mosaic Results Mean
Mosaic results are one of the more confusing parts of PGT-A. Because the biopsy only samples a few cells from the outer layer, the result may not perfectly represent the entire embryo. Some embryos flagged as mosaic could actually be normal, and vice versa. Lower levels of mosaicism are generally associated with better implantation and pregnancy rates, while higher levels of mosaicism may overlap with truly abnormal embryos, making the distinction less reliable.
The American Society for Reproductive Medicine recommends that clinics have clear policies about how mosaic results are reported and managed. In practice, most clinics will prioritize transferring fully normal embryos first, then consider mosaic embryos if no normal embryos are available. Genetic counseling is recommended for anyone weighing whether to transfer a mosaic embryo, and prenatal testing is offered during any resulting pregnancy.
Does PGT-A Improve IVF Success Rates?
This is where the picture gets complicated. When you transfer a single embryo that PGT-A has confirmed is chromosomally normal, per-transfer pregnancy rates are significantly higher. One study of patients under 35 found ongoing pregnancy rates of 69% with tested embryos compared to 42% with embryos selected by appearance alone.
But PGT-A also reduces the total number of embryos available for transfer, because some will come back abnormal. A large 2019 trial across 34 clinics found that cumulative live birth rates were actually slightly lower in the PGT-A group (77.2%) than in the conventional IVF group (81.8%), though the PGT-A group had fewer miscarriages (8.7% vs. 12.6%). The average age in that study was about 29, meaning these were younger patients with generally good prognoses. In one study of an older patient population, only 43.6% of PGT-A cycles produced at least one normal embryo to transfer, and live birth rates per cycle showed no significant difference between tested and untested groups.
The takeaway: PGT-A makes each individual transfer more likely to succeed and reduces miscarriage risk, but it doesn’t guarantee more babies per IVF cycle overall, especially for younger patients who already have good odds. Its value tends to increase with maternal age, when the proportion of abnormal embryos is higher and selecting the right one matters more.
Cost of PGT
PGT is an add-on cost to your IVF cycle. In the United States, the total typically ranges from $3,000 to $6,000 per cycle. That breaks down into two parts: the biopsy procedure itself (around $1,500 to $2,000) and the genetic analysis ($150 to $350 per embryo). The more embryos you have biopsied, the higher the total. Insurance coverage varies widely, and many plans do not cover genetic testing on embryos even when they cover part of IVF.
PGT-M can cost more than PGT-A because the lab often needs to develop a custom test (called a probe) specific to your family’s mutation before the cycle begins. This setup step can add several hundred to a few thousand dollars and takes weeks to prepare, so it needs to be planned well in advance of your egg retrieval.
Who PGT Is Recommended For
PGT-A is most commonly recommended for people over 35, those with a history of recurrent miscarriage, and those who have had multiple failed embryo transfers. It can also be useful when you want to do a single embryo transfer and reduce the chance of transferring an embryo that won’t implant.
PGT-M is specifically for families with a known single-gene disorder. Both partners typically undergo carrier screening first, and if a specific mutation is identified, PGT-M can test embryos for that exact condition. PGT-SR is recommended when either partner has a known chromosomal rearrangement, which is sometimes discovered only after unexplained miscarriages or a referral to a genetic counselor.