At a glance
Understand the key differences between PGT-A for aneuploidy screening and PGT-SR for structural rearrangements, including when each is recommended and how they are performed in Thai laboratories.
Preimplantation genetic testing (PGT) helps identify genetic abnormalities in embryos created through IVF before transfer. Two common types are PGT-A (for aneuploidy) and PGT-SR (for structural rearrangements). While both involve embryo biopsy and genetic analysis, they address different genetic issues. This guide explains the differences, when each is recommended, and what to consider when comparing them in Thailand.
What Is PGT-A?
PGT-A (preimplantation genetic testing for aneuploidy) screens embryos for an abnormal number of chromosomes (aneuploidy). Humans typically have 46 chromosomes (23 pairs). Aneuploidy means an embryo has extra or missing chromosomes, which often leads to implantation failure, miscarriage, or conditions like Down syndrome (trisomy 21). PGT-A checks all 23 pairs of chromosomes for correct number.
What Is PGT-SR?
PGT-SR (preimplantation genetic testing for structural rearrangements) is designed for patients who carry a balanced structural rearrangement in their chromosomes, such as a translocation (Robertsonian or reciprocal) or inversion. These rearrangements do not usually cause health problems for the carrier, but they can lead to unbalanced chromosomes in embryos, increasing the risk of miscarriage or a child with a chromosomal disorder. PGT-SR identifies embryos with balanced or normal chromosomes.
Key Differences Between PGT-A and PGT-SR
| Feature | PGT-A | PGT-SR |
|---|---|---|
| Purpose | Detect aneuploidy (abnormal chromosome number) | Detect unbalanced structural rearrangements |
| Who needs it | Advanced maternal age, recurrent miscarriage, repeated IVF failure, or any patient wanting to reduce aneuploidy risk | Patients known to carry a balanced translocation, inversion, or other structural rearrangement |
| What it analyzes | Number of copies of each chromosome (23 pairs) | Breakpoints and copy number changes across specific chromosome regions |
| Technology | Next-generation sequencing (NGS) or array comparative genomic hybridization (aCGH) | NGS with specific analysis for structural rearrangements; sometimes combined with PGT-A |
| Result categories | Euploid (normal), aneuploid (abnormal), mosaic (mix of normal and abnormal cells) | Balanced/normal, unbalanced (abnormal), or inconclusive |
How Are PGT-A and PGT-SR Performed in Thai Labs?
Both tests require an IVF cycle to create embryos. On day 5 or 6 of development, a few cells are biopsied from the trophectoderm (the part that becomes the placenta). The biopsy is sent to a genetics laboratory for analysis. In Thailand, many IVF clinics partner with accredited genetic labs that use next-generation sequencing (NGS) for PGT-A and PGT-SR. The process is similar, but PGT-SR requires additional bioinformatics to detect breakpoints and unbalanced rearrangements.
Timeline
After biopsy, results typically take 7–14 days. Embryos are frozen (vitrified) while waiting for results. A subsequent frozen embryo transfer (FET) is performed in a later cycle.
When Is Each Recommended?
PGT-A is commonly considered for:
- Women aged 35 or older
- Couples with a history of recurrent miscarriage
- Previous IVF cycles with poor embryo development or implantation failure
- Patients who wish to reduce the chance of transferring an aneuploid embryo
PGT-SR is specifically recommended for:
- Individuals or couples where one partner carries a balanced translocation (Robertsonian or reciprocal)
- Carriers of inversions or other structural rearrangements
- Couples with a history of recurrent miscarriage due to unbalanced chromosomes
Note: PGT-SR is not a routine test for all IVF patients. It is only indicated when a structural rearrangement is known or strongly suspected.
Can PGT-A and PGT-SR Be Combined?
Yes. Many genetic laboratories can perform both tests simultaneously on the same biopsy. This is often called “combined PGT” or “PGT-A+SR.” It screens for both aneuploidy and unbalanced structural rearrangements. This may be beneficial for translocation carriers who also have age-related aneuploidy risk. However, not all clinics offer combined testing; confirm with your clinic.
Limitations and Considerations
- Mosaicism: Both PGT-A and PGT-SR may detect mosaicism (a mix of normal and abnormal cells). Interpretation can be complex, and not all mosaic embryos are abnormal.
- Accuracy: No test is 100% accurate. There is a small risk of misdiagnosis or inconclusive results.
- Embryo loss: Biopsy and freezing may reduce embryo viability slightly, though vitrification techniques have improved outcomes.
- Cost: PGT adds to the overall cost of IVF. PGT-SR may be more expensive due to specialized analysis.
- Not a guarantee: PGT cannot guarantee a healthy baby or prevent all genetic conditions. It only screens for the specific abnormalities tested.
Questions to Ask Your Clinic in Thailand
- Which genetic laboratory do you work with? Is it accredited?
- Do you offer combined PGT-A and PGT-SR?
- What technology is used (NGS, aCGH)?
- How long do results take?
- What is the cost for PGT-A, PGT-SR, and combined testing?
- How are mosaic embryos reported and counseled?
- What is your experience with PGT-SR for translocation carriers?
Next Steps
- Confirm your genetic status: If you have a known translocation or inversion, request a referral for genetic counseling.
- Choose an IVF clinic in Thailand that offers PGT-SR and has experience with structural rearrangements.
- Ask about the specific genetic lab and their success rates with PGT-SR.
- Discuss the possibility of combined PGT-A+SR if you are also concerned about aneuploidy.
- Plan for a frozen embryo transfer cycle after results are available.
For more information, see our PGT in Thailand overview, guides, and FAQ.
Frequently asked questions
Can PGT-A detect structural rearrangements like translocations?
Standard PGT-A screens for chromosome number abnormalities but does not reliably detect balanced structural rearrangements. PGT-SR is specifically designed for that purpose. However, PGT-A may sometimes pick up large unbalanced rearrangements, but it is not a substitute for PGT-SR.
Is PGT-SR necessary for all IVF patients?
No. PGT-SR is only recommended for patients who are known carriers of a balanced translocation, inversion, or other structural rearrangement. It is not a routine test for all IVF patients.
How much does PGT-A and PGT-SR cost in Thailand?
Costs vary by clinic and genetic laboratory. PGT-SR is often more expensive than PGT-A due to specialized analysis. Contact your chosen clinic for exact pricing.
Can PGT-A and PGT-SR be done together?
Yes, many labs offer combined testing (PGT-A+SR) on the same embryo biopsy. This screens for both aneuploidy and unbalanced structural rearrangements. Confirm availability with your clinic.
What is the success rate of PGT-SR for translocation carriers?
Success rates depend on many factors, including the type of translocation, maternal age, and embryo quality. PGT-SR can increase the chance of transferring a chromosomally normal embryo, but it does not guarantee pregnancy or live birth. Discuss expected outcomes with your clinic.
Continue your research
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.
Need help turning research into a shortlist?
