PGT-A vs PGT-SR in Thailand: Key Differences for Patients with Chromosomal Rearrangements

If you are considering IVF with preimplantation genetic testing (PGT) in Thailand, you may encounter two common types: PGT-A and PGT-SR. While both tests analyze embryos before transfer, they look for different genetic issues. PGT-A (aneuploidy screening) checks for an abnormal number of chromosomes, while PGT-SR (structural rearrangement testing) detects changes in chromosome structure, such as translocations or inversions. This article explains the key differences, who may benefit from each test, and what to consider when planning treatment in Thailand.

At a Glance: PGT-A vs PGT-SR

• PGT-A: Screens all 23 pairs of chromosomes for extra or missing chromosomes (aneuploidy). Used for advanced maternal age, recurrent miscarriage, or repeated implantation failure.
• PGT-SR: Detects unbalanced structural rearrangements (e.g., translocations, inversions) in embryos. Recommended for patients who carry a balanced rearrangement themselves.
• Both: Require embryo biopsy and genetic analysis. Results help select euploid (normal) embryos for transfer, potentially improving implantation and reducing miscarriage risk.

What Is PGT-A?

PGT-A (preimplantation genetic testing for aneuploidy) evaluates embryos for the correct number of chromosomes. Aneuploidy—having too many or too few chromosomes—is a leading cause of implantation failure, miscarriage, and conditions like Down syndrome. PGT-A is often recommended for women over 35, couples with recurrent pregnancy loss, or those with multiple failed IVF cycles. The test does not detect structural rearrangements or single-gene disorders.

What Is PGT-SR?

PGT-SR (preimplantation genetic testing for structural rearrangements) is designed for individuals who carry a balanced chromosomal rearrangement, such as a reciprocal or Robertsonian translocation, or an inversion. Carriers are usually healthy but may produce embryos with unbalanced rearrangements, leading to miscarriage or affected offspring. PGT-SR identifies embryos with balanced or normal chromosomes, allowing transfer of those with the best chance of healthy development.

Key Differences Between PGT-A and PGT-SR

Feature	PGT-A	PGT-SR
What it detects	Aneuploidy (extra/missing chromosomes)	Unbalanced structural rearrangements
Who it is for	Advanced maternal age, recurrent miscarriage, repeated IVF failure	Carriers of balanced translocations, inversions, or other structural changes
Genetic cause	Random errors in egg/sperm formation	Inherited or de novo structural change in a parent
Testing method	NGS, aCGH, or SNP array on trophectoderm biopsy	NGS with specific analysis for breakpoints, or aCGH/SNP array
Result categories	Euploid (normal), aneuploid, mosaic	Balanced/normal, unbalanced, inconclusive

Who Should Consider PGT-SR?

PGT-SR is typically offered to couples where one partner has a known balanced chromosomal rearrangement. Common indications include:

• History of recurrent miscarriage
• Previous child with a structural chromosome abnormality
• Known carrier of a translocation or inversion from karyotype testing
• Male factor infertility due to structural rearrangement (e.g., Y chromosome microdeletion)

If you have not had karyotype testing, your doctor may recommend it before considering PGT-SR.

Testing Process in Thailand

The process for both PGT-A and PGT-SR follows similar steps:

1. IVF cycle: Ovarian stimulation, egg retrieval, fertilization (usually ICSI), and embryo culture to blastocyst stage (day 5-6).
2. Embryo biopsy: A few cells are removed from the trophectoderm (future placenta) using a laser. The embryo is then vitrified (frozen).
3. Genetic analysis: Biopsied cells are sent to a genetics laboratory. For PGT-SR, the lab must know the specific rearrangement to design the test.
4. Results: Typically available within 1-2 weeks. A genetic counselor or doctor explains the results and which embryos are suitable for transfer.
5. Frozen embryo transfer: A euploid or balanced embryo is thawed and transferred in a subsequent cycle.

In Thailand, many IVF clinics offer PGT in collaboration with accredited genetic laboratories. Turnaround times and costs vary; confirm details directly with your chosen clinic.

Questions to Ask Your Clinic

• Do you offer both PGT-A and PGT-SR? Which laboratory do you work with?
• How many embryos typically reach the blastocyst stage for biopsy?
• What is the success rate for frozen embryo transfers after PGT?
• How are mosaic embryos (with mixed normal and abnormal cells) handled?
• Is genetic counseling included in the process?
• What are the costs for PGT-A vs PGT-SR, and are there additional fees for transport or storage?

Limitations and Considerations

Neither PGT-A nor PGT-SR guarantees a pregnancy or a healthy baby. Both tests have limitations:

• Embryo biopsy carries a small risk of damage, though modern techniques are safe.
• PGT cannot detect all genetic conditions, such as single-gene disorders (for that, PGT-M is used).
• Mosaicism can lead to inconclusive results.
• PGT-SR requires prior knowledge of the parental rearrangement; if the breakpoints are not well characterized, the test may be less accurate.
• Not all embryos will be suitable for biopsy or freezing; some may not survive the process.

Discuss these limitations with your fertility specialist to make an informed decision.

Next Steps

• If you suspect a chromosomal rearrangement, ask your doctor for a karyotype test.
• Research IVF clinics in Thailand that offer PGT-SR and have experience with structural rearrangements.
• Prepare for a consultation with a list of questions about testing protocols, success rates, and costs.
• Consider genetic counseling to understand the implications of test results.

For more information, explore our PGT in Thailand guide, patient guides, and frequently asked questions.

Frequently asked questions

Can PGT-A detect structural rearrangements like translocations?

No, PGT-A is designed to detect aneuploidy (abnormal chromosome number), not structural rearrangements. PGT-SR is specifically needed to identify unbalanced translocations or inversions.

Do I need PGT-SR if I have a balanced translocation?

PGT-SR is often recommended for carriers of balanced translocations to select embryos with balanced or normal chromosomes, reducing the risk of miscarriage or having a child with a chromosomal disorder. However, not all carriers require PGT; discuss your specific situation with a genetic counselor.

Is PGT-SR available in Thailand?

Yes, many IVF clinics in Thailand offer PGT-SR in collaboration with genetic laboratories. Availability and protocols vary, so confirm directly with the clinic.

How long does it take to get PGT-SR results?

Results typically take 1-2 weeks after embryo biopsy, depending on the laboratory and the complexity of the rearrangement.

What is the difference between balanced and unbalanced translocation?

A balanced translocation means the chromosome material is rearranged but no genetic material is lost or gained; carriers are usually healthy. An unbalanced translocation results in extra or missing genetic material, which can cause miscarriage or birth defects.

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.