PGT-A and Embryo Mosaicism: What Do Mosaic Results Mean?

If you have received a mosaic embryo result after PGT-A, you may be wondering what it means for your fertility journey. Mosaicism is a term used when an embryo has a mix of cells with different chromosomal makeups. This guide explains mosaicism in plain language, how it is reported, and what options you might consider. It is important to discuss your specific results with a genetic counselor and your fertility clinic, as every situation is unique.

At a Glance

• Mosaic embryos have both normal and abnormal cells.
• PGT-A reports mosaicism as a percentage range, but the exact percentage may vary.
• Mosaic results are not a guarantee of success or failure.
• Options include transferring the embryo, further testing, or discarding, but decisions are personal and medical.
• Always consult a genetic counselor to understand your specific results.

What Is PGT-A?

Preimplantation Genetic Testing for Aneuploidy (PGT-A) is a test that screens embryos created through IVF for chromosomal abnormalities. It is not a diagnostic test for all genetic conditions, but it can help identify embryos with an abnormal number of chromosomes, which may affect implantation or development.

PGT-A is optional and not suitable for everyone. It is often considered by people who have experienced recurrent miscarriage, have had previous failed IVF cycles, or are of advanced maternal age. However, the decision to use PGT-A should be made with your doctor, who can explain the potential benefits and limitations based on your history.

What Is Embryo Mosaicism?

Mosaicism occurs when an embryo contains two or more cell populations with different chromosomal content. For example, some cells may have the typical 46 chromosomes, while others may have an extra or missing chromosome. This is different from a uniformly abnormal embryo, where all cells have the same abnormality.

Mosaicism can arise during cell division after fertilization. The degree of mosaicism is often described as a percentage, such as 20% or 60%, indicating the proportion of abnormal cells. However, this percentage is an estimate based on the biopsy sample and may not reflect the entire embryo.

How Are Mosaic Results Reported?

PGT-A results are typically categorized as:

• Euploid: All cells tested have the expected number of chromosomes.
• Aneuploid: All cells tested have an abnormal number of chromosomes.
• Mosaic: A mix of normal and abnormal cells is detected.

Mosaic results may be further described as low, medium, or high level, depending on the proportion of abnormal cells. The exact reporting criteria can vary between laboratories, so it is important to ask your clinic how they interpret and report mosaicism.

What Do Mosaic Results Mean for Your Embryo?

A mosaic result does not mean the embryo is definitely abnormal or definitely normal. The clinical significance of mosaicism is still being studied. Some mosaic embryos may self-correct during development, while others may not implant or may lead to miscarriage. In some cases, a mosaic embryo can result in a healthy baby, but this is not guaranteed.

It is also important to note that PGT-A is a screening test, not a diagnostic test. It cannot detect all chromosomal abnormalities, and a mosaic result does not provide a definitive answer about the embryo’s potential.

Options After a Mosaic Result

If you receive a mosaic result, you may have several options, but these depend on your clinic’s policies, your medical history, and local regulations. Possible options include:

• Transfer the mosaic embryo: Some clinics may offer transfer, especially if the mosaicism is low-level. However, this decision involves careful counseling about potential risks and outcomes.
• Further testing: You might consider additional genetic testing, such as PGT-M or PGT-SR, if there is a specific genetic concern. However, these tests are for specific conditions and may not clarify mosaicism.
• Discard the embryo: Some patients choose not to transfer a mosaic embryo, but this is a personal decision.
• Consider another IVF cycle: You may decide to undergo another cycle to create more embryos for testing.

It is crucial to discuss these options with your fertility specialist and a genetic counselor. They can provide guidance based on the latest research and your individual circumstances.

Questions to Ask Your Clinic

When discussing your mosaic result, consider asking the following questions:

• What is the exact level of mosaicism reported, and how does your lab define low, medium, or high?
• What is your clinic’s policy on transferring mosaic embryos?
• What are the potential risks and outcomes associated with transferring this embryo?
• Are there any additional tests that could provide more information?
• What support services are available, such as genetic counseling?

Next Steps

After receiving a mosaic result, take time to process the information. Schedule a consultation with your clinic and a genetic counselor to discuss your options in detail. Remember that you are not alone, and many people face similar decisions. Seek support from your medical team and loved ones as you navigate this complex situation.

For more information about PGT in Thailand, visit our PGT in Thailand page. You may also find our guides and FAQ sections helpful.

Frequently asked questions

Can a mosaic embryo result in a healthy baby?

Yes, there have been cases where mosaic embryos have led to healthy live births, but this is not guaranteed. The outcome depends on the specific chromosomal abnormality, the level of mosaicism, and other factors. It is important to discuss your specific situation with a genetic counselor.

Is a mosaic embryo considered abnormal?

A mosaic embryo has both normal and abnormal cells, so it is not classified as uniformly normal or abnormal. The clinical significance is uncertain, and it may behave differently depending on the proportion of abnormal cells and which chromosomes are affected.

Should I transfer a mosaic embryo?

The decision to transfer a mosaic embryo is personal and should be made with your fertility doctor and genetic counselor. They can help you weigh the potential risks and benefits based on your medical history and the specific characteristics of the embryo.

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

PGT-A screens for chromosomal abnormalities (aneuploidy), while PGT-M tests for specific single-gene disorders when one or both parents carry a known genetic mutation. They are different tests used for different purposes.

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.