Georgia PGT-SR Chromosome Screening Technology: Suitable Populations and Detailed Procedure

A Real Consultation: Why Her Chromosome Report Directly Led the Doctor to Recommend PGT-SR

Three weeks ago, a 35-year-old woman walked into the consultation room with her and her husband's karyotype analysis reports. The wife's karyotype was normal, while the husband's was 45,XY,der(13;14)(q10;q10) – a Robertsonian translocation carrier. They had already experienced two spontaneous miscarriages, and the third embryo stopped developing at 8 weeks of gestation. She asked, "Can IVF in Georgia prevent another miscarriage? Why did the doctor directly recommend PGT-SR instead of standard PGT-A?"

This is one of the most common scenarios I encounter in my overseas assisted reproduction coordination work. For carriers of chromosomal structural rearrangements, standard PGT-A (aneuploidy screening) cannot accurately identify embryos with unbalanced chromosomes because PGT-A only detects chromosome number, not segmental structure. PGT-SR is specifically designed for this purpose and is already a routine technology in several reproductive centers in Georgia with genetic laboratories.

PGT-SR Chromosome Screening Technology: Core Definition and Applicable Conditions

When is PGT-SR Suitable?

PGT-SR (Preimplantation Genetic Testing for Structural Rearrangements) is suitable for the following populations:

• One or both partners are carriers of chromosomal balanced translocations (including reciprocal translocations, Robertsonian translocations)
• Known carriers of chromosomal inversions (e.g., paracentric inversion, pericentric inversion)
• History of multiple spontaneous miscarriages due to chromosomal imbalance (requires confirmation by couple's karyotype analysis that one partner is a structural rearrangement carrier)
• Family history of chromosomal structural rearrangements with confirmed high risk through genetic counseling
• In some cases, couples with normal karyotypes but recurrent miscarriages where embryo copy number variation (CNV) testing suggests rearrangement structural abnormalities

When is PGT-SR Not Suitable?

• Only due to advanced maternal age (female age ≥38) or poor egg quality causing aneuploidy – PGT-A should be chosen in this case
• Both partners have completely normal karyotypes with no history of recurrent miscarriage or family genetic history – PGT-SR is meaningless
• Known very low ovarian reserve in older women (AMH <0.5 ng/mL, basal antral follicle count <3) – may not yield enough embryos for biopsy
• Chromosomal structural rearrangement but pregnancy has been confirmed feasible through prenatal diagnosis (e.g., amniocentesis), and the patient does not accept the potential embryo loss from biopsy

Why PGT-SR is Different from PGT-A: Starting from Genetic Principles

During gamete formation, carriers of chromosomal structural rearrangements produce a large number of unbalanced gametes (sperm or eggs). For example, reciprocal translocation carriers theoretically produce over 50% of gametes carrying deleted or duplicated chromosome segments. Embryos formed after fertilization with these unbalanced gametes often stop developing early or lead to miscarriage. PGT-A uses low-coverage whole-genome sequencing (e.g., NGS) only to determine if the number of each chromosome is normal and cannot identify segmental imbalances. PGT-SR, on the other hand, uses high-resolution aCGH (array comparative genomic hybridization) or SNP array to precisely detect copy number changes in chromosome segments and can locate breakpoint regions. The mainstream platforms used in Georgia are the Illumina HumanCytoSNP-12 array or custom NGS panels, which can simultaneously perform PGT-A and PGT-SR.

Complete Process of PGT-SR in Georgia

Step 1: Pre-procedure Preparation and Genetic Testing Confirmation

Complete chromosome karyotype analysis reports (G-banding ≥550 bands) for both partners must be provided. It is recommended to complete this 2 months before departure. If only low-resolution karyotypes (<320 bands) have been done, they need to be redone. Some centers require simultaneous preparation of peripheral blood DNA testing (e.g., FISH verification of breakpoints) to design probes for embryo testing.

Step 2: Ovarian Stimulation and Egg Retrieval (Female)

Antagonist or long protocol is used, chosen by the Georgia reproductive doctor based on AMH, FSH, and age. After egg retrieval, ICSI is the preferred fertilization method to avoid interference from unclear sperm fragments.

Step 3: Embryo Culture and Biopsy

Embryos are cultured to the blastocyst stage on day 5-6. Trophectoderm biopsy (5-10 cells) is performed on blastocysts that meet the criteria for biopsy (at least expanded blastocyst with clear inner cell mass and trophectoderm). Laboratories in Georgia are typically equipped with laser-assisted hatching and cell aspiration devices; high biopsy experience is required.

Step 4: Genetic Analysis (aCGH or SNP array)

After whole genome amplification of the biopsied cells, high-density chip scanning is used. Analysis time is approximately 3-7 working days. Results are categorized as: chromosomally normal/balanced embryos (transferable), unbalanced embryos (non-transferable), and some uncertain results requiring re-biopsy or discard. SNP array, in addition to analyzing copy number variations, can also detect contamination such as uniparental disomy.

Step 5: Frozen-Thawed Embryo Transfer

After the test results are available, transferable embryos are selected. Usually, all embryos are frozen and the endometrial cycle is prepared for transfer. No re-biopsy is needed before transfer. Blood β-hCG is tested 12-14 days after transfer.

How Long Does It Take: Complete Cycle Timeline

• From registration to egg retrieval: Approximately 2-4 weeks (depends on the woman's menstrual cycle and stimulation protocol)
• Embryo biopsy + genetic analysis: Approximately 1-2 weeks
• Transfer cycle preparation: Endometrial preparation takes about 2 weeks (natural cycle or hormone replacement cycle)
• Complete single cycle (stimulation to transfer): Approximately 6-8 weeks
• If multiple stimulation cycles are needed to accumulate embryos, the total time extends to 3-6 months

Risks and Important Considerations

Technical Risks:

• Potential impact of biopsy on embryos: The post-biopsy blastocyst survival rate is about 5% lower than non-biopsied embryos, but data from Georgia centers show that experienced laboratories can control this within 1-3%.
• Missed detection or misdiagnosis: In rare cases, due to highly repetitive regions in the chromosomal rearrangement, insufficient chip probe coverage may lead to false negatives. This is particularly noteworthy when breakpoints are in centromeric coding regions. It is advisable to ask the laboratory about the historical detection rate for that specific translocation type during genetic counseling.
• Inability to distinguish between balanced translocation carriers and completely normal embryos: Standard aCGH cannot distinguish between a balanced translocation (carrier) and a completely normal karyotype because the copy number is identical. If differentiation is needed, additional targeted testing (e.g., breakpoint PCR) is required. Most centers consider balanced translocation carriers to be developmentally normal and transferable.

Procedural Risks:

• Risk of no available normal embryos – for some complex translocations, the proportion of normal/balanced embryos may be less than 10%, requiring multiple stimulation cycles.
• Embryo chromosomal abnormalities are not solely caused by structural rearrangements – advanced maternal age may also contribute to aneuploidy, increasing the difficulty of obtaining normal embryos.

Practitioner Observations: Two Most Overlooked Details

In my liaison work in Georgia, I have found that over 60% of patients overlook two points during their first consultation:

• Chromosome karyotype resolution must be sufficient. Some domestic hospitals routinely issue reports with around 400 bands, which may miss small translocations. It is recommended to request ≥550 bands, and preferably also provide FISH verification. There have been cases where insufficient karyotype resolution led to PGT-SR probe design failure, wasting a stimulation cycle.
• Differences in testing turnaround times among Georgia laboratories. Some centers use external laboratories (e.g., sending samples to CMT Lab in Tbilisi or Genomed in Moscow), which adds an extra 3-4 days for sample transport; while centers with in-house laboratories can provide results within 5 days. It is advisable to inquire about this before choosing a center.

Frequently Asked Questions: What Real Patients Care About Most

Q1: What is the approximate cost of PGT-SR in Georgia?

Costs are charged per embryo: biopsy + analysis is approximately $800-$1500 per embryo (depending on the center and technology platform). Ovarian stimulation and transfer packages are additional. The total cycle cost is typically between $15,000 and $25,000. Compared to the US ($40,000-$60,000), it offers a price advantage, but attention should be paid to differences in technical expertise.

Q2: If I have already had PGT-A but miscarried, should I switch to PGT-SR?

If there is a clear chromosomal structural rearrangement in the couple, switching to PGT-SR is necessary. Conversely, if the couple's karyotypes are normal, it may be due to low-level mosaicism or cryptic translocations. In this case, high-resolution PGT-A + CNV analysis is more recommended rather than directly targeting structural abnormalities.

Q3: Does PGT-SR affect embryo quality?

Biopsy itself adds stress to the embryo, but for embryos that have reached the blastocyst stage, the impact is limited. Data from Georgia centers: the survival rate of vitrified blastocysts after biopsy is about 95%, and the live birth rate is not statistically different from non-biopsied blastocysts (provided the laboratory is qualified).

Special Case Management: When One Partner is a Structural Rearrangement Carrier and the Other is Normal

This is the most common scenario. For example, the wife is normal, and the husband is a balanced translocation carrier. In this case, PGT-SR only needs to analyze the chromosomes involved in the husband's translocation (the 2 related chromosome segments). The remaining chromosomes can be screened using the same chip for PGT-A. However, note: if both partners are under 35 years old and have no other risk factors, screening only for the translocation-related imbalance is sufficient, without performing whole-genome CNV on all chromosomes, to reduce testing costs. Georgia centers typically offer tiered options: a basic version (only chromosomes related to the structural abnormality) and a complete version (whole genome + PGT-SR).

Risk Reminder: Non-negligible Aspects When Choosing Georgia

Although Georgia opened up early in the field of assisted reproduction, PGT-SR requires high laboratory hardware and software standards. Before deciding, it is recommended to confirm the following three points:

• Whether the center is equipped with a high-resolution aCGH platform (resolution ≤50 kb) and has professional genetic analysts;
• Whether there is a specific wet lab protocol for chromosomal structural rearrangements (e.g., quality control standards after WGA);
• Whether English or Chinese genetic counseling report interpretation services are provided (some patients, due to language barriers, fail to understand the meaning of "uncertain segments" in the test report in time, leading to incorrect transfer decisions).

PGT-SR is not a panacea – even after transferring a chromosomally normal embryo, there is still a chance of early pregnancy failure due to uterine factors or immune factors. It is recommended to communicate with a reproductive immunology specialist before starting the cycle to rule out other causes of recurrent miscarriage. Every step should be based on real evidence, not marketing rhetoric.