Preimplantation Genetic Testing: PGT-A and PGT-M Explained

Preimplantation genetic testing is an IVF laboratory technique used to assess embryos for certain genetic or chromosomal concerns before transfer. PGT-A and PGT-M serve different purposes, and understanding the difference helps patients make informed decisions with their fertility specialist and genetic counselor.

Overview

Preimplantation genetic testing, often called PGT, is a group of laboratory tests used during in vitro fertilization (IVF) to assess embryos before they are transferred to the uterus. The testing is performed on a small number of cells taken from an embryo, most commonly at the blastocyst stage, which usually develops several days after fertilization. The goal is to provide additional information that may help doctors and patients choose which embryo to transfer.

The two most commonly discussed forms are PGT-A and PGT-M. PGT-A stands for preimplantation genetic testing for aneuploidy. It screens embryos for missing or extra chromosomes. PGT-M stands for preimplantation genetic testing for monogenic or single-gene disorders. It is used when there is a known inherited condition in a family, such as a specific gene mutation that could be passed to a child.

Although the names sound similar, PGT-A and PGT-M answer different questions. PGT-A asks whether an embryo appears to have the expected number of chromosomes. PGT-M asks whether an embryo has inherited a particular gene change. Neither test evaluates every possible health condition, and neither guarantees implantation, pregnancy, or the birth of a baby without medical problems.

PGT-A Explained

PGT-A examines the number of chromosomes in embryo cells. Humans typically have 46 chromosomes arranged in 23 pairs. An embryo with an extra or missing chromosome is described as aneuploid. Aneuploidy is a common reason embryos may not implant, may lead to miscarriage, or may result in certain chromosomal conditions.

In IVF, embryos that appear healthy under the microscope can still have chromosomal differences. PGT-A provides genetic information beyond embryo appearance, which may help the fertility team prioritize embryos for transfer. It is most often considered for patients of advanced maternal age, those with repeated pregnancy loss, prior IVF cycles without success, or when there are multiple embryos and additional selection information may be helpful.

PGT-A results are commonly reported as euploid, aneuploid, mosaic, or sometimes no result. A euploid result means the tested cells showed the expected chromosome number. Aneuploid means an abnormal chromosome number was detected. Mosaic means the tested sample suggests a mixture of chromosomally normal and abnormal cells. A no-result or inconclusive result may occur if the sample does not provide enough reliable DNA information.

It is important to understand that PGT-A is a screening test, not a perfect diagnosis of the entire embryo. Because only a few cells are tested, results may not fully represent all cells in the embryo. For this reason, patients should review the benefits, limits, and possible outcomes with their IVF specialist before deciding whether PGT-A fits their situation.

PGT-M Explained

PGT-M is used to test embryos for a specific inherited genetic condition when the disease-causing gene change is already known. This may apply when one or both intended parents are carriers of a genetic condition, when a parent has a dominant genetic disorder, or when there is a family history of a serious inherited disease. Examples may include cystic fibrosis, spinal muscular atrophy, sickle cell disease, thalassemia, Huntington disease, or certain hereditary cancer syndromes, depending on the exact family mutation.

Unlike PGT-A, which looks broadly at chromosome number, PGT-M is customized for the family. Before IVF begins, the laboratory usually needs genetic reports from the intended parents and sometimes relatives. This preparation allows the lab to design a test that can identify which embryos have inherited the specific gene variant of concern.

PGT-M can help patients avoid transferring embryos affected by the condition being tested. Depending on the inheritance pattern, embryos may be classified as unaffected, affected, or carriers. In some conditions, carrier embryos may be healthy but able to pass the gene variant to future generations. The meaning of each result depends on the condition and should be explained by a genetic counselor or specialist.

PGT-M does not test for all genetic diseases unless those conditions are specifically included and technically validated. It may also be performed together with PGT-A in some IVF cycles, allowing both single-gene and chromosome-number information to be considered. This combined approach should be discussed carefully, as it may affect cost, timing, and the number of embryos considered suitable for transfer.

Who May Consider Preimplantation Genetic Testing?

Preimplantation genetic testing is not required for every IVF cycle. It is an option that may be recommended or considered based on medical history, age, family history, previous pregnancy outcomes, and personal values. The decision is individualized, and patients should have time to ask questions before consenting to testing.

PGT-A may be discussed when there is a higher likelihood of embryo aneuploidy or when information about chromosome number may help guide embryo transfer decisions. PGT-M is usually considered when a specific inherited disease risk has been identified before IVF. Some patients learn about this risk through carrier screening, previous affected pregnancies, known family history, or genetic testing after a relative is diagnosed.

Situations where PGT may be discussed include:

• Known carrier status for a serious inherited condition
• A parent affected by a single-gene disorder that may be passed to children
• Previous pregnancy or child affected by a genetic condition
• Recurrent miscarriage or recurrent IVF implantation failure
• Advanced maternal age, depending on clinic policy and patient goals
• A known parental chromosomal rearrangement, which may require PGT-SR rather than PGT-A or PGT-M

Emotional, ethical, financial, and cultural factors can also influence the decision. Some patients feel reassured by additional information, while others may prefer not to test embryos. A respectful fertility team should explain the options clearly and support informed decision-making without pressure.

How the Testing Process Works

PGT is performed as part of an IVF cycle. The process begins with ovarian stimulation to help the ovaries produce multiple eggs. After egg retrieval, eggs are fertilized with sperm in the laboratory. Embryos are then cultured for several days until they reach the stage at which biopsy is appropriate, most often the blastocyst stage.

During embryo biopsy, a trained embryologist removes a few cells from the trophectoderm, the part of the blastocyst that later contributes to the placenta. The inner cell mass, which develops into the fetus, is not the usual biopsy target. After biopsy, embryos are commonly frozen while the genetic laboratory analyzes the sampled cells. This is why PGT cycles often involve a frozen embryo transfer rather than a fresh transfer.

The laboratory report is then reviewed by the fertility specialist, and in many cases by a genetic counselor. If suitable embryos are available, the care team discusses transfer planning. The embryo selected for transfer may depend on PGT results, embryo quality, patient age, uterine preparation, medical history, and patient preferences.

The timeline can vary. PGT-M may require additional preparation before the IVF cycle because the test is tailored to the family. PGT-A usually requires less pre-cycle customization, but results still take time after embryo biopsy. Patients should ask their clinic how long testing usually takes and what happens if results are inconclusive or if no transferable embryos are identified.

Benefits, Limitations, and Safety Considerations

The main benefit of PGT is that it provides information before embryo transfer. For PGT-M, this can significantly reduce the chance of transferring an embryo affected by the specific condition tested. For PGT-A, the information may help prioritize embryos with the expected chromosome number, which can be useful when deciding which embryo to transfer first.

However, PGT has important limitations. It does not improve the genetic quality of an embryo; it only tests a small sample of cells. It cannot guarantee that an embryo will implant, that a pregnancy will continue, or that a child will be free of all health conditions. Some embryos may produce no result, and mosaic results can be complex to interpret.

Embryo biopsy and freezing are widely used in modern IVF laboratories, but they require advanced expertise and careful quality control. The potential risks are considered low in experienced laboratories, yet they are not zero. Patients should ask about the clinic’s laboratory experience, how embryos are biopsied and frozen, and how results are communicated.

Even after PGT, prenatal care remains important. Many professional organizations advise that prenatal screening or diagnostic testing, such as chorionic villus sampling or amniocentesis when appropriate, should still be discussed during pregnancy. This is because PGT is performed before pregnancy and cannot replace all forms of prenatal evaluation.

Counseling, Decision-Making, and Emotional Support

Genetic testing in IVF can bring hope, but it can also create difficult decisions. Some patients may receive fewer suitable embryos than expected, mosaic results, or no transferable embryos in a cycle. Others may need to decide whether to transfer a carrier embryo, retest an embryo, repeat IVF, use donor eggs or sperm, or consider other family-building options.

Genetic counseling is especially valuable for PGT-M, because inheritance patterns can be complex. A counselor can explain the condition being tested, the chance of passing it on, what different embryo results mean, and what prenatal testing may still be recommended. Counseling can also help patients think through ethical questions in a calm and structured way.

Patients can prepare for discussions by asking practical questions: What exactly is being tested? What results are possible? How accurate is the test for this family? What happens if the embryo result is mosaic or inconclusive? How will embryos be stored, and what choices exist for embryos not selected for transfer?

Acibadem International’s multidisciplinary fertility, genetics, and obstetric teams support international patients in the diagnosis and treatment planning of IVF-related genetic concerns within JCI-accredited hospitals. Patients considering treatment abroad should also ask about legal requirements, documentation, embryo storage rules, and follow-up care in their home country.

When to Speak With a Fertility Specialist

Patients should speak with a fertility specialist if they are planning IVF and have questions about whether PGT-A or PGT-M is appropriate. Early consultation is particularly important when there is a known inherited condition, because PGT-M often requires test development before the IVF cycle begins. Bringing existing genetic reports can help the team provide more precise guidance.

A consultation is also recommended for couples with recurrent miscarriage, repeated unsuccessful IVF cycles, advanced reproductive age, or a previous pregnancy affected by a chromosomal or genetic condition. In these situations, the doctor may recommend genetic counseling, parental karyotyping, carrier screening, or other evaluations before deciding on the most suitable testing strategy.

Patients should seek medical advice promptly if they are already pregnant after PGT and are unsure which prenatal tests are recommended. The obstetrician and genetic counselor can explain screening and diagnostic options, their timing, and what information each test can provide. This supports safe, continuous care from fertility treatment through pregnancy.

Frequently asked questions

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

PGT-A screens embryos for missing or extra chromosomes. PGT-M tests embryos for a specific single-gene condition known to be present in a family. PGT-A is a broader chromosome-number screen, while PGT-M is a targeted test designed around a known genetic variant.

Does PGT guarantee a successful pregnancy?

No. PGT can provide helpful genetic information, but it cannot guarantee implantation, prevent miscarriage in all cases, or ensure the birth of a healthy baby. Embryo quality, uterine health, age, medical conditions, and many other factors still affect IVF outcomes.

Can PGT detect all genetic diseases?

No. PGT-A looks at chromosome number, not every gene. PGT-M can test for a specific known gene change, but it does not automatically screen for all inherited conditions unless specific testing is designed and validated.

Is embryo biopsy harmful?

Embryo biopsy is commonly performed in experienced IVF laboratories and is generally considered low risk. However, it is a delicate procedure and cannot be described as risk-free. Patients should discuss laboratory experience, biopsy technique, and embryo freezing practices with their clinic.

What does a mosaic embryo result mean?

A mosaic result suggests that the tested cells may include a mixture of chromosomally normal and abnormal cells. Interpretation can be complex because the biopsy sample may not represent the entire embryo. Decisions about mosaic embryos should be made with a fertility specialist and genetic counselor.

Is prenatal testing still needed after PGT?

Prenatal screening or diagnostic testing may still be recommended after pregnancy is achieved. PGT tests only a small number of embryo cells before pregnancy and cannot replace all prenatal evaluations. The obstetrician or genetic counselor can explain which tests are appropriate.

How should patients prepare for PGT-M?

Patients should gather any available genetic test reports for themselves and affected relatives, if possible. A genetic counselor or specialist will confirm the exact condition and inheritance pattern. The laboratory may need time to create a customized test before the IVF cycle begins.

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.