What are the Types of PGT Testing Used in IVF?

Not all genetic testing in IVF is the same. Preimplantation genetic testing (PGT) is an umbrella term that covers several distinct laboratory procedures, each designed to answer a different clinical question about an embryo's genetic makeup. Understanding the types of PGT testing available, what each one detects, and when it may be appropriate is an important part of making informed decisions about IVF treatment.

The different types of preimplantation genetic testing (PGT) share a common foundation: a small number of cells are biopsied from a blastocyst-stage embryo and sent to a genetics laboratory for analysis. Beyond that shared process, however, PGT-A, PGT-M, and PGT-SR are meaningfully different in what they look for, how the laboratory analysis is performed, and which patients are most likely to benefit.

This article explains each type clearly, addresses common questions about testing accuracy, costs, and risks, and outlines how a specialist can help determine which approach is most relevant to an individual's circumstances.

The Three Main Types of PGT Testing

PGT-A: Testing for Chromosomal Aneuploidy

PGT-A, or preimplantation genetic testing for aneuploidy, is the most commonly used form of PGT in IVF. It examines whether an embryo has the correct number of chromosomes. Humans typically have 46 chromosomes arranged in 23 pairs. An embryo with too many or too few chromosomes is described as aneuploid, and chromosomal aneuploidy is one of the leading causes of failed implantation, early miscarriage, and conditions such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13).

PGT-A screens all 24 chromosome types and identifies embryos that appear chromosomally normal, referred to as euploid. These embryos are generally prioritized for transfer, as euploid embryos have a statistically higher likelihood of resulting in a successful implantation and ongoing pregnancy than untested embryos from the same cohort.

The likelihood of chromosomal aneuploidy in embryos increases with age, which is why PGT-A is often discussed with patients of advanced maternal age. It is also relevant for patients who have experienced recurrent pregnancy loss or repeated IVF failure without a clear explanation, as chromosomal abnormalities in embryos are a common underlying factor in both.

PFCLA's clinical team provides a detailed overview of PGT-A and related preimplantation genetic screening services for patients seeking more information about how this testing is applied in practice.

PGT-M: Testing for Monogenic or Single-Gene Disorders

PGT-M, or preimplantation genetic testing for monogenic disorders, is used when one or both partners carry a known mutation associated with a specific heritable condition. Unlike PGT-A, which surveys all chromosomes for numerical abnormalities, PGT-M is highly targeted. It is designed to detect a single, pre-identified genetic variant in embryos before transfer.

Conditions for which PGT-M may be used include cystic fibrosis, sickle cell disease, Tay-Sachs disease, Huntington's disease, spinal muscular atrophy, and hereditary cancer syndromes linked to BRCA1 and BRCA2 mutations, among many others. The specific mutation must be known and characterized in advance, and the laboratory must develop a customized testing protocol before the IVF cycle begins. This preparatory phase typically adds several weeks to the overall timeline.

PGT-M can significantly reduce the probability of an embryo carrying two copies of a recessive mutation, or a dominant mutation, depending on the inheritance pattern of the condition in question. It does not screen for all possible genetic variants simultaneously, and it does not replace carrier screening for conditions that have not yet been identified in a patient's personal or family history.

For patients who are uncertain whether they carry heritable variants, preconception carrier screening is a separate and important first step. This article on common misconceptions about genetic carrier screening addresses some of the confusion patients often encounter around this process.

PGT-SR: Testing for Structural Chromosomal Rearrangements

PGT-SR, or preimplantation genetic testing for structural rearrangements, is used when one or both partners carry a chromosomal rearrangement such as a translocation or inversion. In these cases, the overall amount of chromosomal material may be normal, but segments of chromosomes have been repositioned in a way that can result in embryos with unbalanced chromosomal arrangements.

Patients who carry balanced translocations often have no health problems themselves, but their embryos face a higher risk of inheriting unbalanced chromosomal material, which can lead to miscarriage or developmental differences. PGT-SR identifies which embryos carry a balanced or normal chromosomal arrangement and are therefore more suitable for transfer.

PGT-SR is less commonly discussed than PGT-A or PGT-M, but for patients with a confirmed structural rearrangement it can be a particularly meaningful form of testing. A reproductive specialist or genetic counselor can assess whether PGT-SR is relevant based on karyotyping results.

PGT-A and Comprehensive Chromosome Screening: Understanding the Relationship

Patients researching types of PGT testing may encounter the term comprehensive chromosome screening (CCS), and it is worth clarifying how this relates to PGT-A. CCS is not a separate category of testing; rather, it refers to the analytical methodology used to perform chromosomal screening. Earlier generations of preimplantation genetic screening examined only a subset of chromosomes. Comprehensive chromosome screening examines all 24 chromosome types simultaneously, which is now standard practice in modern PGT-A.

The platform used for analysis has evolved considerably over time. Next-generation sequencing (NGS) is now widely used in reputable laboratories and offers high resolution across all chromosomes. When evaluating fertility clinics and their laboratory partnerships, patients may find it useful to ask which analytical platform is used and whether the laboratory holds relevant accreditations such as CAP (College of American Pathologists) certification or CLIA (Clinical Laboratory Improvement Amendments) compliance.

How the Biopsy Process Works Across All PGT Types

Regardless of which type of PGT testing is performed, the embryo biopsy process follows the same fundamental approach. Once embryos have developed to the blastocyst stage, typically five to seven days after fertilization, a small number of cells (usually around five) are carefully removed from the trophectoderm, which is the outer cell layer that later develops into the placenta. The inner cell mass, which develops into the fetus, is not disturbed.

The biopsy is performed by a skilled embryologist and is generally considered to carry a low risk of harm to the embryo when carried out by an experienced team. Following biopsy, embryos are cryopreserved while the cellular samples are sent to the genetics laboratory for analysis. Results typically return within one to two weeks, after which the care team reviews findings with the patient and discusses the implications for embryo transfer.

One question patients often raise is whether the biopsy itself could reduce the chances of a successful pregnancy. Current evidence from well-designed studies suggests that, when performed by experienced practitioners, trophectoderm biopsy does not significantly compromise embryo viability or pregnancy outcomes. That said, it is a procedure with a small margin of technical risk, and patients should feel comfortable asking their clinical team about the embryology team's experience and biopsy outcomes.

How Many Embryos Are Typically Needed for PGT?

This is a question with no single answer, because the proportion of embryos that test as suitable for transfer varies considerably between patients. Factors that influence this include age, ovarian reserve, the cause of infertility, and whether any specific genetic condition is being screened for.

In general terms, a larger cohort of embryos going into testing increases the likelihood that at least one euploid or unaffected embryo will be identified. For patients of advanced maternal age, the proportion of aneuploid embryos tends to be higher, which means more embryos may be needed to yield one suitable for transfer. For patients using PGT-M to screen for a recessive condition where both partners are carriers, statistically around one in four embryos would be expected to be affected.

These probabilities are important to understand in advance, not to create anxiety, but to help set realistic expectations about how many IVF cycles may be needed and to inform the conversation about how many embryos to aim for in a given stimulation cycle.

Benefits and Limitations of PGT Testing

Each type of PGT testing offers distinct potential benefits within an IVF cycle, and a clear understanding of those benefits sits alongside an equally clear understanding of their limits.

On the benefit side, PGT-A has been associated with higher implantation rates per transfer for euploid embryos compared to untested embryos in the same age group, and with reduced rates of early miscarriage attributable to chromosomal causes. PGT-M can meaningfully reduce the risk of conceiving a child affected by a specific known genetic condition. PGT-SR can reduce the rate of miscarriage in patients with structural rearrangements by identifying more viable embryos for transfer.

On the limitations side, several important points deserve emphasis. PGT-A does not detect all genetic conditions, only chromosomal aneuploidy. A euploid result does not guarantee implantation or a healthy live birth. PGT-M is highly specific to a known variant and does not provide broader genetic screening. Mosaicism, where an embryo contains a mixture of chromosomally normal and abnormal cells, can produce results that are difficult to interpret and that require careful individualized clinical discussion. False positive and false negative results, while uncommon in accredited laboratories, remain a possibility.

A thoughtful, patient-centered discussion of these trade-offs is available in this overview of the pros and cons of PGS and PGT-A testing, which addresses many of the practical considerations patients weigh when deciding whether testing is appropriate for them.

Which Type of PGT Testing Is Right for a Specific Situation?

The answer depends on the individual's clinical picture, and it is one of the most important conversations to have with a reproductive specialist before committing to a testing approach. Some general principles apply:

• PGT-A is most commonly recommended for patients of advanced maternal age, those with a history of recurrent pregnancy loss or repeated IVF failure, and those who wish to maximize the information available before a single embryo transfer.
• PGT-M is recommended when a specific heritable single-gene condition has been identified in one or both partners, or when carrier screening has revealed that both partners carry variants for the same recessive condition.
• PGT-SR is recommended when karyotyping has confirmed that one or both partners carry a chromosomal structural rearrangement.
• In some cases, more than one type of testing may be appropriate simultaneously, for example PGT-A and PGT-M in a patient who is both a carrier of a single-gene disorder and of advanced maternal age.

A genetic counselor can play an important role in helping patients understand which testing approach is most relevant to their specific history. Their involvement is particularly valuable when a heritable condition is in the picture, but they can also help clarify what carrier screening results mean and how they should inform treatment planning.

The Cost of Different Types of PGT Testing

Cost is a practical consideration that shapes many patients' decisions about whether and how to pursue genetic testing. The expenses associated with PGT vary by type, and several components typically contribute to the overall cost.

For PGT-A, costs generally include the embryo biopsy procedure, laboratory analysis per embryo, and the clinical consultation involved in reviewing results. PGT-M tends to be more expensive than PGT-A because of the advance laboratory preparation required to develop a customized testing protocol for a specific mutation. PGT-SR pricing varies depending on the complexity of the rearrangement being analyzed.

Insurance coverage for any type of PGT testing varies considerably by provider and plan. Some insurers cover genetic testing when there is documented medical necessity, such as confirmed carrier status or a history of recurrent pregnancy loss. In other cases, it is treated as an elective expense. This breakdown of PGT-A testing costs provides a more detailed overview of what patients typically encounter when budgeting for genetic testing as part of IVF. Fertility clinics often have financial counselors available to help navigate coverage questions and available financing options.

Discussing PGT Testing Options with a Specialist

Choosing between the types of PGT testing, or deciding whether to pursue testing at all, is a decision that deserves individualized clinical input. The most appropriate approach depends on factors that are specific to each patient: their age, medical and family history, carrier status, reproductive history, and personal priorities. There is no universal recommendation that applies across all circumstances.

Pacific Fertility Center Los Angeles works with patients across a wide range of genetic and reproductive backgrounds, providing evidence-based guidance on PGT testing as part of a comprehensive and personalized approach to IVF care. If you have questions about which types of preimplantation genetic testing may be relevant to your situation, or if you would like to discuss your treatment options with a specialist, the PFCLA team is here to help. Reaching out to schedule a consultation is a straightforward first step toward getting the clarity you need.