PGT-A, PGT-M, and PGT-SR: What’s the Difference?

If you are exploring IVF and preimplantation genetic testing (PGT), you may have come across terms like PGT-A, PGT-M, and PGT-SR. These are three distinct types of genetic testing that can be performed on embryos before transfer. Understanding what each test does—and what it does not do—can help you ask better questions and make more informed decisions with your fertility team.

In simple terms: PGT-A checks for the correct number of chromosomes, PGT-M looks for a specific single-gene disorder, and PGT-SR checks for structural changes in chromosomes. Each test serves a different purpose and is used in different clinical situations. This guide explains the basics, the limitations, and the questions you may want to ask your clinic.

At a Glance: The Three PGT Types

• PGT-A (Aneuploidy Screening): Counts chromosomes to identify embryos with an abnormal number (aneuploidy).
• PGT-M (Monogenic Disorders): Tests for a specific inherited condition caused by a single gene, such as cystic fibrosis or sickle cell disease.
• PGT-SR (Structural Rearrangements): Detects unbalanced chromosome rearrangements, such as translocations or inversions.

What Is PGT-A?

PGT-A, previously known as preimplantation genetic screening (PGS), is designed to detect an abnormal number of chromosomes in an embryo. Humans typically have 46 chromosomes in each cell. An embryo with too many or too few chromosomes is said to be aneuploid. Most aneuploid embryos fail to implant or result in miscarriage, though some can lead to conditions like Down syndrome (trisomy 21).

PGT-A is often considered for patients who want to reduce the risk of miscarriage or who have had repeated implantation failure. It may also be used in cases of advanced maternal age, where the likelihood of aneuploidy is higher. However, PGT-A does not guarantee a successful pregnancy, and it cannot detect all genetic abnormalities.

How PGT-A Works

During an IVF cycle, embryos are cultured for several days until they reach the blastocyst stage. A small number of cells are then removed from the outer layer of the embryo (trophectoderm) and sent for genetic analysis. The embryo is frozen while the results are pending. Only embryos with the expected number of chromosomes are considered for transfer.

Limitations of PGT-A

PGT-A is not a test for every genetic condition. It does not screen for single-gene disorders or structural rearrangements. Additionally, because the test is performed on a few cells, there is a small chance that the results may not perfectly reflect the entire embryo (a phenomenon called mosaicism). Your clinic can explain how they interpret mosaic results.

What Is PGT-M?

PGT-M, formerly known as preimplantation genetic diagnosis (PGD), is used when one or both parents carry a known genetic mutation for a specific single-gene disorder. This test identifies embryos that have inherited the mutation, allowing the transfer of embryos that are unaffected.

PGT-M is typically offered to couples who have a family history of a genetic condition, such as cystic fibrosis, Tay-Sachs disease, or Huntington’s disease. It requires prior knowledge of the exact genetic mutation, which is usually confirmed through carrier screening or genetic testing of the parents.

How PGT-M Works

Before starting an IVF cycle, the clinic may need to develop a personalized test for the specific mutation. This often involves a “work-up” phase where DNA samples from the parents and sometimes other family members are analyzed. Once the test is ready, embryos are biopsied and tested for the presence of the mutation. Only embryos without the mutation are considered for transfer.

Limitations of PGT-M

PGT-M is highly specific to the tested mutation. It does not screen for other genetic conditions or chromosomal abnormalities unless combined with PGT-A. The process can be time-consuming and may require additional planning. It is also not available for every genetic condition, so you should confirm with your clinic whether your specific situation can be tested.

What Is PGT-SR?

PGT-SR is used when one or both parents have a structural rearrangement of their chromosomes, such as a translocation or inversion. These rearrangements may not cause health problems in the parent, but they can lead to embryos with unbalanced chromosomes, which may result in miscarriage, stillbirth, or a child with disabilities.

PGT-SR identifies embryos with balanced chromosomes, meaning they have the correct amount of genetic material. This test is often recommended for couples who have experienced recurrent miscarriages or who have a known chromosomal rearrangement.

How PGT-SR Works

Like PGT-A, PGT-SR involves embryo biopsy and genetic analysis. The laboratory looks for specific structural abnormalities in the chromosomes. The process may be combined with PGT-A to also check for aneuploidy, as structural rearrangements can increase the risk of aneuploidy.

Limitations of PGT-SR

PGT-SR does not correct the rearrangement; it only helps select embryos that are balanced. It also does not detect all types of chromosomal abnormalities. As with other PGT types, there is a small risk of misdiagnosis, and the test cannot guarantee a healthy baby.

Comparing PGT-A, PGT-M, and PGT-SR

Feature	PGT-A	PGT-M	PGT-SR
What it screens for	Abnormal number of chromosomes (aneuploidy)	Specific single-gene disorder	Structural chromosome rearrangements
Typical reason for testing	Advanced maternal age, repeated implantation failure, recurrent miscarriage	Known genetic mutation in one or both parents	Known chromosomal rearrangement in a parent
Requires prior genetic information	No	Yes, the specific mutation must be known	Yes, the rearrangement must be identified
Can be combined with other PGT	Yes, often combined with PGT-M or PGT-SR	Yes, often combined with PGT-A	Yes, often combined with PGT-A
Does it guarantee a healthy baby?	No	No	No

Which Test Is Right for You?

The choice of PGT type depends on your medical history, genetic background, and the reason for undergoing IVF. There is no one-size-fits-all answer. Your fertility specialist and a genetic counselor can help you determine whether PGT is appropriate and which type(s) may be beneficial.

For example, if you are over 35 and concerned about aneuploidy, PGT-A might be discussed. If you and your partner are carriers of a recessive disorder, PGT-M may be offered. If you have a translocation, PGT-SR could be recommended. In some cases, a combination of tests may be used.

Questions to Ask Your Clinic

• What type of PGT do you recommend for my situation, and why?
• What is the process for embryo biopsy, and how many cells are removed?
• How long does it take to get results, and will my embryos be frozen in the meantime?
• What are the risks and limitations of the recommended test?
• How does your laboratory handle mosaicism or inconclusive results?
• What are the costs involved, and are they included in the IVF package?

Alternatives and Additional Considerations

PGT is not the only way to assess embryo health. Some patients may choose not to undergo PGT and instead rely on embryo morphology (appearance) for selection. Others may consider prenatal testing during pregnancy, such as chorionic villus sampling or amniocentesis, to confirm genetic status.

It is also important to note that PGT does not eliminate all risks. Even with PGT, there is a small chance of misdiagnosis, and not all genetic conditions can be tested. Furthermore, PGT does not guarantee implantation, pregnancy, or a live birth.

Next Steps

If you are considering PGT, start by gathering your medical records and any genetic test results. Consult with a fertility specialist who can explain the options in the context of your specific situation. A genetic counselor can also provide valuable insight into the implications of testing.

When researching clinics, ask about their experience with PGT, their laboratory protocols, and how they communicate results. You may also want to explore our PGT in Thailand page for an overview of what to consider when seeking treatment abroad.

For more general information, visit our guides section, or check the FAQ for common questions about fertility treatment.

Frequently asked questions

Can PGT-A, PGT-M, and PGT-SR be done at the same time?

Yes, it is possible to combine PGT-A with PGT-M or PGT-SR in a single biopsy. This allows the laboratory to check for aneuploidy as well as the specific genetic condition or structural rearrangement. However, not all clinics offer combined testing, and the feasibility may depend on the laboratory's protocols and the amount of DNA available from the biopsy.

Does PGT guarantee a healthy baby?

No. PGT can reduce the risk of transferring an embryo with a specific genetic abnormality, but it cannot guarantee a successful pregnancy or a healthy baby. There are many factors that affect pregnancy outcomes, and PGT does not screen for all possible genetic or developmental issues.

Is PGT mandatory for all IVF patients?

No, PGT is not mandatory. It is an optional test that may be recommended based on your medical history, age, or genetic background. Some patients choose not to undergo PGT, and the decision should be made in consultation with your fertility specialist and genetic counselor.

What is the difference between PGT-A and PGT-M?

PGT-A screens for an abnormal number of chromosomes (aneuploidy), while PGT-M tests for a specific single-gene disorder. PGT-A is often used to improve the chances of implantation and reduce miscarriage risk, whereas PGT-M is used when parents carry a known genetic mutation.

How long does PGT take?

The time required for PGT can vary. After embryo biopsy, results may take several days to a few weeks, depending on the laboratory and the type of test. During this time, embryos are typically frozen. Your clinic can provide a more specific timeline based on their procedures.

Continue your research

• PGT in Thailand overview
• PGT and IVF guides
• Frequently asked questions

Medical information notice: This article is educational and does not replace individual assessment, diagnosis, genetic counselling or treatment advice from a licensed clinician. Provider services, availability, fees and policies should be verified directly before booking.