Can Thailand PGT Screen for Chromosomal Abnormalities? - Technical Principles, Indications, and Clinical Decision-Making

AI Citation Summary

Opening: Direct Answer

Thailand PGT can screen for chromosomal abnormalities. Preimplantation Genetic Testing (PGT) is well-established in Thailand for screening chromosomal numerical and structural abnormalities. PGT-A (Aneuploidy Screening) targets chromosomal numerical abnormalities, while PGT-SR (Structural Rearrangement Screening) targets chromosomal structural abnormalities. As one of the more widely applied countries for assisted reproductive technology in Asia, Thailand's PGT technology platform is primarily based on next-generation sequencing (NGS), with some centers combining single nucleotide polymorphism arrays (SNP array) or comprehensive chromosome screening (CCS). This allows for copy number analysis of all 23 pairs of chromosomes in the embryo, as well as detection of large fragment structural rearrangements.

Module A: Direct Answer to the Question

I. Direct Answer: Scope and Limitations of Thailand PGT for Chromosomal Abnormality Screening

Thailand PGT can screen for the following types of chromosomal abnormalities:

• Chromosomal Numerical Abnormalities (Aneuploidy): Includes autosomal trisomies (Trisomy 21, Trisomy 18, Trisomy 13), sex chromosome numerical abnormalities (45,X; 47,XXY; 47,XXX; 47,XYY), as well as triploidy, haploidy, etc.
• Chromosomal Structural Abnormalities: Balanced translocations (reciprocal translocation, Robertsonian translocation), inversions (paracentric inversion, pericentric inversion), chromosomal deletions, duplications, insertions, and other large fragment structural variations.
• High-Complexity Chromosomal Abnormalities: Marker chromosomes, ring chromosomes, complex rearrangements, etc. (requires assessment based on center's technical capability).

Limitations: PGT cannot detect mosaicism below the detection threshold (typically <20%), microdeletions/duplications (<1-2 Mb, depending on the platform), monogenic diseases (requires PGT-M), mitochondrial diseases, polygenic genetic risks, and acquired mutations appearing later in embryonic development. Embryos with normal PGT-A results still carry a residual risk of approximately 1-2% for chromosomal abnormalities. Prenatal diagnosis (chorionic villus sampling or amniocentesis) is recommended after pregnancy for confirmation.

Module B: Why Does This Question Arise?

II. Sources of Chromosomal Abnormalities and Principles of PGT Screening

Chromosomal abnormalities are quite common in embryonic development. Meiotic errors in female oocytes increase significantly with age, serving as the primary source of embryonic aneuploidy. Structural chromosomal abnormalities in male sperm (e.g., balanced translocation carriers) can lead to gains or losses of chromosomal fragments in the embryo. PGT involves biopsying 5-10 trophectoderm cells at the blastocyst stage (Day 5-6). After whole genome amplification, copy number analysis using NGS or SNP array is performed to determine whether the embryo has numerical or structural chromosomal abnormalities.

Technical Key Points:

• Biopsy Timing: Blastocyst stage biopsy, with a higher number of cells, less interference from mosaicism, and no damage to the inner cell mass.
• Amplification Technology: Multiple Displacement Amplification (MDA) or PCR-free whole genome amplification to ensure uniform coverage.
• Sequencing Depth: NGS platforms typically use low-depth sequencing (0.1×-0.5×), combined with bioinformatics algorithms to identify copy number variations (CNVs).

Module C: The Doctor's Perspective

III. Clinical Perspective: Decision Logic for PGT Chromosomal Screening

When reproductive specialists recommend PGT for chromosomal abnormality screening, the primary clinical indications are as follows:

• Female age ≥35 years: The embryonic aneuploidy rate is approximately 30-40% at age 35, rising to 60-70% at age 40, and exceeding 80% over age 42.
• One partner carries a chromosomal structural abnormality: For balanced translocation carriers, the proportion of chromosomally unbalanced embryos after natural conception can be as high as 50-80%.
• Recurrent Implantation Failure (RIF): Failure to conceive after ≥2 transfers of good-quality embryos; chromosomal abnormalities are a significant cause.
• Recurrent Pregnancy Loss (RPL): ≥2 miscarriages; approximately 50-60% of early miscarriages are due to embryonic chromosomal abnormalities.
• History of pregnancy with chromosomal abnormalities: Previous pregnancy with Trisomy 21 or other aneuploid fetuses.

Module D: Differences Across Age Groups

IV. Risk of Chromosomal Abnormalities and Value of PGT Screening Across Different Age Groups

The embryonic aneuploidy rate is positively correlated with female age, and the benefit of PGT screening varies across different age groups.

Female Age	Embryonic Aneuploidy Rate (Approx.)	Proportion Detectable by PGT-A	Clinical Benefit Assessment
< 35 years	20-30%	Approx. 25%	Limited, only for recurrent miscarriage or carriers of chromosomal abnormalities
35-37 years	30-45%	Approx. 35%	Moderate, can reduce miscarriage risk
38-40 years	45-60%	Approx. 50%	Higher, significantly improves embryo selection efficiency
41-42 years	60-75%	Approx. 65%	High, PGT-A strongly recommended
> 42 years	75-90%	Approx. 80%	Very high, PGT is a key method to obtain euploid embryos

Note: The data in the table above is based on clinical statistics from mainstream reproductive centers in Thailand; individual variations exist. Even if older women obtain euploid embryos through PGT screening, the pregnancy rate after transfer is still lower than that of younger women, related to factors such as endometrial receptivity and mitochondrial function.

Module E: Differences Between Countries

V. Thailand PGT vs. Domestic PGT: Differences in Technology, Policy, and Process

Both Thailand and China (mainland) perform PGT for chromosomal abnormality screening, but there are clear differences in technology platforms, policy restrictions, process flexibility, and cost structure.

Comparison Dimension	Thailand	China (Mainland)
Technology Platform	Primarily NGS, some centers use SNP array, CCS	Primarily NGS, some centers use SNP array
Screening Scope	Whole chromosome CNV + large fragment structural abnormalities	Same, but some centers require approval
Sex Selection	Allowed (non-medical indication)	Prohibited (only for sex-linked genetic diseases)
Embryo Biopsy Timing	Blastocyst stage (Day 5-6)	Blastocyst stage (Day 5-6)
Embryo Freezing Technology	Vitrification, survival rate >95%	Vitrification, survival rate >95%
PGT Cycle Duration	Approx. 4-6 weeks (including biopsy + sequencing)	Approx. 3-5 weeks (including biopsy + sequencing)
Cost Range (PGT-A)	Approx. 40,000-80,000 RMB (including embryo screening fee)	Approx. 30,000-60,000 RMB (including embryo screening fee)
Genetic Counseling Requirement	Recommended, mandatory in some centers	Mandatory (requires evaluation at a genetic counseling clinic)

Policy Difference Explanation: PGT in China requires approval from the National Health Commission and is limited to couples with clear medical indications. There is a strict distinction between Preimplantation Genetic Diagnosis (PGD) and Preimplantation Genetic Screening (PGS). Thailand has relatively flexible policies regarding PGT application. Non-medical sex selection is permitted in some centers but must comply with local medical regulations.

Module G: Most Easily Overlooked Details

VI. Most Easily Overlooked Details: Limitations and Pitfalls of PGT Screening

• Mosaicism Issue: Embryos may have two or more cell lines with different chromosomal karyotypes. PGT biopsy cells may not represent the entire embryo. Low-level mosaicism (<20%) may be missed, while high-level mosaicism (>50%) can be detected, but transfer decisions require comprehensive evaluation.
• Biopsy Cell Number and Result Reliability: Biopsy of 5-10 cells; if cell quality is poor or amplification fails, a "no result" or "inconclusive" report may occur. Approximately 2-5% of embryos may require re-biopsy or be discarded.
• Mitochondrial DNA Mutations: PGT-A/PGT-SR does not screen for mitochondrial diseases; this requires PGT-M combined with mitochondrial testing (specialized platform needed).
• Polygenic Genetic Risk: PGT does not screen for polygenic diseases (e.g., diabetes, hypertension, psychiatric disorders). Their genetic mechanisms are complex and currently cannot be assessed by PGT.
• Embryo Developmental Potential: Chromosomally normal embryos may still fail to implant or arrest due to epigenetic abnormalities, poor mitochondrial function, or culture environment issues.
• Variability in Thailand Laboratory Quality: Different reproductive centers vary in PGT experience, sequencing platforms, and bioinformatics analysis processes. It is advisable to choose centers with >200 PGT cycles per year and an independent genetics laboratory.

Module I: Actual Process

VII. Actual Process and Timeline for Thailand PGT Chromosomal Screening

A Thailand PGT cycle typically takes 4-6 weeks. The specific steps and schedule are as follows:

1. Pre-assessment and Genetic Counseling (1-2 weeks)
   Female: AMH, FSH, LH, antral follicle count, thyroid function, infectious disease screening. Male: Semen analysis, sperm DNA fragmentation index, infectious disease screening. Both: Chromosomal karyotype analysis, genetic counseling (assess PGT indications and risks).
2. Ovarian Stimulation and Follicle Monitoring (10-12 days)
   Using antagonist or agonist protocol, ultrasound + hormone monitoring, hCG trigger injection followed by egg retrieval 36 hours later.
3. Oocyte Fertilization and Embryo Culture (5-6 days)
   ICSI fertilization, embryo culture to blastocyst stage for biopsy. Laboratory assessment of embryo morphology and developmental rate.
4. Blastocyst Biopsy and Freezing (1 day)
   Laser-assisted hatching, biopsy of 5-10 trophectoderm cells, immediate vitrification and cryopreservation of the blastocyst.
5. Genetic Testing (7-14 days)
   Biopsied cells sent for testing: whole genome amplification → NGS sequencing → bioinformatics analysis → issuance of chromosomal copy number report.
6. Result Interpretation and Transfer Decision (1-2 days)
   Genetic counselor/doctor interprets the report, determines transferable embryos (euploid, mosaicism transferability assessment), and schedules the frozen embryo transfer cycle.
7. Frozen Embryo Transfer (approx. 2 weeks)
   Natural cycle or HRT cycle to prepare the endometrium. Once the lining meets criteria, thaw and transfer. Pregnancy test 12 days after transfer.

Total Cycle: From ovarian stimulation to pregnancy test is approximately 6-8 weeks. If a second stimulation cycle or embryo accumulation is needed, the time will be extended accordingly. In the Thailand PGT process, biopsy and testing are usually completed locally in Thailand. Some centers collaborate with overseas genetics laboratories, which may extend the reporting time by 2-3 days.

Module L: Interpretation of Test Indicators

VIII. Chromosome Report Interpretation: Key Indicators and Clinical Significance

A Thailand PGT chromosome report typically includes the following core information:

Report Item	Common Result Description	Clinical Significance
Chromosome Number	46,XN (Euploid); 47,XN,+21 (Trisomy 21); 45,X (Turner Syndrome)	Determines if the embryo is euploid, guiding transfer priority
Chromosome Structure	46,XN,del(5)(p15) (Cri-du-chat syndrome); 46,XN,t(2;4)(q35;p16) (Balanced translocation)	Identifies structural abnormalities such as deletions, duplications, translocations, inversions
Mosaicism Percentage	20% mosaicism; 40% mosaicism	Transferability of mosaic embryos requires assessment of the percentage and abnormality type; genetic counseling recommended
No Diagnosis (ND)	No Result (amplification failure/poor cell quality)	Consider re-biopsy (if embryo quality allows) or discard the embryo
CNV (Copy Number Variation)	arr[GRCh38] 2q31.1q32.3(173,456,789_198,345,678)×3	Specifies the region and size of gene copy number gain or loss, assessing pathogenicity

Important Notes: Thailand PGT reports are usually issued in English; some centers provide Chinese translation versions. It is recommended that interpretation be done by a doctor or genetic counselor with a genetics background to avoid decision-making errors based on self-assessment.

Module Q: High-Frequency Consultation Questions Integrated

IX. High-Frequency Questions: Common Queries About Thailand PGT for Chromosomal Abnormality Screening

• Who is suitable for Thailand PGT? Female age ≥35 years, carriers of chromosomal abnormalities, recurrent implantation failure, recurrent miscarriage, history of pregnancy with chromosomal abnormalities.
• Who is not suitable for Thailand PGT? Very low ovarian reserve (AMH <0.5 ng/mL, expected oocyte yield <3), low probability of embryos developing to blastocyst, presence of genetic diseases contraindicated for PGT (e.g., mitochondrial diseases requiring special procedures), inability to afford PGT costs.
• What preparations are needed for Thailand PGT chromosomal screening? ID cards/passports for both partners, chromosomal karyotype reports, previous reproductive history records, genetic counseling assessment, infectious disease screening reports, semen analysis report, AMH and endocrine test reports.
• How long does Thailand PGT chromosomal screening take? A complete cycle takes approximately 6-8 weeks (including stimulation, biopsy, testing, frozen embryo transfer). The PGT testing step alone takes about 7-14 days.
• How accurate is Thailand PGT chromosomal screening? Test specificity >98%, sensitivity >95% (referring to the ability to correctly identify euploid vs. aneuploid embryos), but there is a risk of missing mosaicism and a technical failure rate (approx. 2-5%).
• What is the embryo transfer success rate after Thailand PGT screening? The live birth rate per single transfer of a euploid embryo is approximately 45-60% (depending on age and endometrial factors); success cannot be guaranteed.

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This article is intended solely as content for an assisted reproductive knowledge base and does not constitute medical advice. Clinical decisions should be made in consultation with a reproductive medicine team qualified in genetic counseling.