PGT in IVF: Embryo Genetic Testing, Benefits, and Limits

Preimplantation genetic testing, or PGT, is an embryo genetic testing option used during IVF to assess certain chromosomal or inherited genetic risks before embryo transfer. It can be helpful for selected patients, but it has important limits and should be discussed with a fertility specialist and, when appropriate, a genetic counselor.

Overview

PGT in IVF stands for preimplantation genetic testing. It is a group of laboratory tests used to examine embryos created through in vitro fertilization before an embryo is selected for transfer to the uterus. The goal is to provide more information about the embryo’s genetic makeup so doctors and patients can make an informed decision about which embryo to transfer.

In a typical IVF treatment cycle, eggs are collected from the ovaries and fertilized with sperm in the laboratory. Embryos are then grown for several days, often to the blastocyst stage. If PGT is planned, a trained embryologist removes a small number of cells from the outer layer of the embryo, called the trophectoderm. These cells are sent for genetic analysis, while the embryo is usually frozen and stored safely until results are available.

PGT is not one single test. The main types are PGT-A, PGT-M, and PGT-SR. PGT-A assesses whether an embryo has the expected number of chromosomes. PGT-M is used when there is a known risk of a specific single-gene condition in the family. PGT-SR is used when one parent carries a structural chromosome rearrangement, such as a balanced translocation. Each type has a different purpose, benefit, and limitation.

Types of PGT: PGT-A, PGT-M, and PGT-SR

PGT-A, or preimplantation genetic testing for aneuploidy, looks for embryos with missing or extra chromosomes. Humans usually have 46 chromosomes arranged in 23 pairs. Embryos with an abnormal number of chromosomes are less likely to implant and more likely to result in miscarriage or certain chromosomal conditions. PGT-A is sometimes considered for patients of advanced maternal age, those with repeated pregnancy loss, or those with repeated unsuccessful embryo transfers, although its value can vary from person to person.

PGT-M, or preimplantation genetic testing for monogenic disorders, is used when there is a known inherited condition caused by a specific gene change. Examples include conditions such as cystic fibrosis, thalassemia, sickle cell disease, Huntington disease, or certain hereditary cancer predisposition syndromes. Before PGT-M can be performed, the exact genetic change in the family must usually be identified. A customized test may then be developed for that couple or individual.

PGT-SR, or preimplantation genetic testing for structural rearrangements, is considered when a parent carries a chromosome rearrangement, such as a reciprocal translocation, Robertsonian translocation, inversion, or other balanced rearrangement. The parent may be healthy, but embryos can inherit unbalanced chromosome material, which may reduce implantation chances or increase miscarriage risk. PGT-SR helps identify embryos with a balanced or normal chromosome pattern according to the test’s capability.

These tests do not replace standard prenatal care. Even after PGT, patients may be offered prenatal screening or diagnostic testing during pregnancy, such as ultrasound assessments, noninvasive prenatal testing, chorionic villus sampling, or amniocentesis, depending on the situation and medical guidance.

How PGT Is Performed During IVF

PGT requires an IVF cycle because embryos must be created and observed in the laboratory before testing. Ovarian stimulation medications are used to help several eggs mature. After egg retrieval, eggs are fertilized with sperm, often using intracytoplasmic sperm injection, or ICSI, especially when genetic testing is planned. ICSI may reduce the chance that extra sperm DNA around the embryo interferes with the genetic result, though laboratory protocols vary.

Embryos are monitored for several days. Many clinics perform embryo biopsy at the blastocyst stage, usually around day 5, 6, or sometimes 7 after fertilization. The embryologist removes a few cells from the trophectoderm, which later contributes to the placenta, rather than from the inner cell mass, which develops into the fetus. The biopsy is delicate and requires experience, but it is widely used in modern IVF laboratories.

After biopsy, embryos are commonly frozen using vitrification while the genetic laboratory analyzes the cell sample. Results may classify embryos differently depending on the test and reporting system. For example, PGT-A may report embryos as euploid, aneuploid, mosaic, or inconclusive. The fertility team then reviews the results together with embryo quality, patient history, and personal preferences to plan a transfer.

• Euploid: The tested cells show the expected chromosome number.
• Aneuploid: The tested cells show missing or extra chromosomes.
• Mosaic: The tested sample suggests a mixture of cells with different chromosome findings.
• Inconclusive: The laboratory could not obtain a reliable result, and re-biopsy may or may not be considered.

Potential Benefits of PGT

The main benefit of PGT is additional information. For some patients, this information can help prioritize embryos for transfer and may reduce the likelihood of transferring an embryo affected by the specific genetic issue being tested. For couples with a known single-gene condition, PGT-M can be a meaningful way to reduce the chance of having a child affected by that condition, while still using their own eggs and sperm if medically appropriate.

PGT-A may help identify embryos with the expected chromosome number, which can be useful when several embryos are available. In some patients, transferring a euploid embryo may reduce the chance of miscarriage related to chromosomal aneuploidy and may help avoid repeated transfers of embryos with a low chance of implantation. It can also support single embryo transfer decisions, which helps reduce the risks associated with twin or higher-order pregnancies.

PGT-SR can be especially helpful for people with structural chromosome rearrangements. These patients may produce a higher proportion of embryos with unbalanced chromosome material. Testing can help identify embryos more suitable for transfer, potentially reducing the emotional and physical burden of repeated pregnancy loss or unsuccessful transfers.

PGT may also help some patients feel more prepared and informed during fertility care. However, emotional reassurance should not be confused with certainty. Results are powerful tools, but they are one part of a broader clinical picture that includes age, ovarian reserve, sperm health, uterine health, embryo development, and general medical wellbeing.

Limits, Risks, and Ethical Considerations

PGT has important limitations. It cannot guarantee that an embryo will implant, that pregnancy will continue, or that a baby will be born without health conditions. Many aspects of pregnancy and child development cannot be assessed through PGT. A euploid result means the tested cells had the expected chromosome number; it does not mean every possible genetic or medical issue has been excluded.

There is also a small possibility of inaccurate or incomplete results. Embryo mosaicism can make interpretation more complex because the few cells tested may not fully represent the entire embryo. Some embryos may receive an inconclusive result. In rare situations, an embryo may be labeled unsuitable when it might have had developmental potential, or a tested embryo may still have an undetected issue. For this reason, results should be interpreted by experienced fertility specialists and genetics professionals.

PGT may reduce the number of embryos available for transfer. Some embryos may not reach the blastocyst stage, some may not survive biopsy and freezing, and some may return results that are not recommended for transfer. This can be particularly relevant for patients with a low number of embryos. In such cases, the benefit of testing must be weighed carefully against the possibility that there may be no embryo to transfer in that cycle.

Ethical and legal considerations also matter. Rules about embryo testing, storage, transfer, and sex selection differ across countries. Patients may face difficult decisions if results show genetic findings or mosaicism. A respectful, non-directive counseling approach helps patients make choices that align with medical guidance, local law, and personal values.

Who May Consider PGT?

PGT is not automatically recommended for every person undergoing IVF. It may be considered when there is a clear medical reason or when the expected benefits outweigh the limitations. A fertility specialist reviews the patient’s age, ovarian reserve, number of embryos expected, previous IVF outcomes, pregnancy history, and family history before advising whether testing is suitable.

PGT-M is generally considered when one or both partners carry a known gene change that could cause a serious inherited condition in a child. This often requires preparation before the IVF cycle begins, including genetic testing of the parents and sometimes other family members. PGT-SR may be considered when a chromosome rearrangement is known or suspected after recurrent miscarriage, infertility evaluation, or previous prenatal testing.

PGT-A is more individualized. It may be discussed for patients of advanced reproductive age, those with recurrent pregnancy loss, repeated implantation failure, or patients who have several good-quality embryos and want additional information for embryo selection. However, it may be less helpful when only one or very few embryos are available, because the test may not change the treatment plan and may add cost, time, and emotional complexity.

People being evaluated for infertility or female infertility may also need assessment of factors that PGT cannot address, such as ovulation problems, tubal disease, endometriosis, uterine abnormalities, sperm parameters, or hormonal conditions. PGT is best viewed as one possible tool within a complete fertility evaluation rather than a stand-alone solution.

Preparing for PGT and Understanding Results

Preparation begins with a detailed consultation. Patients should ask which type of PGT is being recommended, why it is being recommended, what the alternatives are, and how results may affect embryo transfer decisions. When PGT-M or PGT-SR is planned, genetic counseling is especially important. The counselor can explain inheritance patterns, test accuracy, possible outcomes, and what prenatal testing may still be advised during pregnancy.

Patients should also understand the practical timeline. Some PGT-M cases require weeks or longer to design a family-specific test before ovarian stimulation starts. After embryo biopsy, results may take time, and embryo transfer is usually scheduled in a later frozen embryo transfer cycle. This can feel slower than a fresh transfer, but it allows time for careful testing and planning.

Questions that may be helpful include: What happens if all embryos are abnormal or inconclusive? Can a mosaic embryo be considered for transfer? Will re-biopsy ever be advised? What prenatal testing is recommended after pregnancy? How does the clinic handle embryo storage and consent? Clear answers before the cycle can reduce uncertainty later.

Near the end of decision-making, patients may also consider where they feel most supported. Acibadem International’s multidisciplinary fertility and genetics teams, within JCI-accredited hospitals, diagnose and treat fertility conditions for international patients, including IVF cycles where embryo genetic testing may be appropriate.

When to See a Fertility or Genetics Specialist

A consultation is recommended before IVF if a patient or partner has a known inherited condition, is a carrier of a serious genetic disorder, has a child or previous pregnancy affected by a genetic condition, or has a known chromosome rearrangement. Early referral is useful because some tests require preparation before an IVF cycle can begin.

Patients may also benefit from specialist advice if they have experienced recurrent pregnancy loss, repeated unsuccessful IVF transfers, or are considering IVF at an older reproductive age. These situations do not always mean PGT is needed, but they are good reasons to review whether genetic testing could add useful information.

It is also appropriate to seek support after receiving PGT results that are unexpected, inconclusive, or emotionally difficult. Mosaic results, no euploid embryos, or results showing an inherited condition can raise complex questions. A fertility doctor and genetic counselor can explain the options in a balanced way, including another IVF cycle, transfer considerations where legally and medically appropriate, use of donor gametes, adoption, or choosing not to continue treatment.

Frequently asked questions

What is PGT in IVF?

PGT in IVF is preimplantation genetic testing performed on embryos created in an IVF laboratory. A few cells are usually biopsied from a blastocyst-stage embryo and tested for specific chromosome or genetic findings. The results help guide embryo selection, but they do not guarantee pregnancy or a healthy baby.

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

PGT-A checks whether an embryo has the expected number of chromosomes, while PGT-M tests for a specific inherited single-gene condition known to run in a family. PGT-A is a broader chromosome screening test, whereas PGT-M is customized to a defined genetic risk. The reasons for using each test are different.

Does PGT improve IVF success for everyone?

No, PGT does not improve success for every patient. It may be useful in selected situations, such as known genetic risk, certain chromosome rearrangements, or when several embryos are available for selection. For patients with very few embryos, the benefits may be limited and should be discussed carefully.

Can PGT detect all genetic diseases?

PGT cannot detect all genetic diseases or all possible health conditions. It only tests for the chromosome or genetic issues included in the specific test ordered. Standard prenatal care and, when recommended, prenatal screening or diagnostic testing remain important after pregnancy occurs.

Is embryo biopsy safe?

Embryo biopsy is commonly performed in experienced IVF laboratories, especially at the blastocyst stage. However, it is still a delicate procedure and may carry a small risk to embryo survival or development. The potential benefit of testing should be weighed against this risk for each patient.

What does a mosaic embryo result mean?

A mosaic result means the tested cells suggest a mixture of cells with different chromosome patterns. Interpretation can be complex because the biopsy sample may not fully represent the whole embryo. Decisions about mosaic embryo transfer require careful counseling, clinic policy review, and attention to local regulations.

Is genetic counseling necessary before PGT?

Genetic counseling is strongly recommended for PGT-M and PGT-SR because the results involve inherited conditions or chromosome rearrangements. It can also be helpful for PGT-A, especially when patients need to understand mosaic, inconclusive, or unexpected results. Counseling supports informed and personalized decision-making.

References

• European Society of Human Reproduction and Embryology
• American Society for Reproductive Medicine
• American College of Obstetricians and Gynecologists
• Human Fertilisation and Embryology Authority
• International Committee for Monitoring Assisted Reproductive Technologies

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.