At a glance
Preimplantation Genetic Testing for Structural Rearrangements (PGT-SR) can identify embryos with balanced or unbalanced translocations and inversions. This article explains how PGT-SR works, its limitations, and what patients with known rearrangements should discuss with their clinic in Thailand.
What Are Structural Chromosomal Rearrangements?
Structural chromosomal rearrangements are changes in the structure of chromosomes, such as translocations (where segments of chromosomes swap places) or inversions (where a segment is reversed). These rearrangements can be balanced (no net gain or loss of genetic material) or unbalanced (leading to extra or missing material). Carriers of balanced rearrangements are often healthy but may have an increased risk of infertility, miscarriage, or having a child with chromosomal abnormalities.
What Is PGT-SR?
Preimplantation Genetic Testing for Structural Rearrangements (PGT-SR) is a specialized genetic test performed on embryos created through IVF. It is designed to detect embryos that carry unbalanced rearrangements, which can cause implantation failure, miscarriage, or genetic disorders. PGT-SR can also identify embryos with balanced rearrangements, though the clinical significance of a balanced carrier embryo is generally considered similar to that of the parent carrier.
How Does PGT-SR Work?
PGT-SR typically uses a technique called next-generation sequencing (NGS) or array comparative genomic hybridization (aCGH) to analyze the entire genome of a few cells biopsied from an embryo. By mapping the chromosomal segments, the test can identify whether the embryo has inherited the rearrangement in a balanced or unbalanced form. The accuracy depends on the size and location of the rearrangement, as well as the laboratory’s expertise.
Who Should Consider PGT-SR?
PGT-SR is an option for couples where one or both partners are known carriers of a structural rearrangement, such as a reciprocal or Robertsonian translocation, or an inversion. It is also considered for couples with a history of recurrent miscarriage, failed IVF cycles, or a previous child with an unbalanced rearrangement. However, PGT-SR is not a guarantee of a healthy pregnancy or live birth, and it is not suitable for all patients.
Limitations of PGT-SR
- Detection limits: Very small rearrangements may not be detectable with standard PGT-SR platforms. The laboratory should confirm the resolution of their test for the specific rearrangement.
- Balanced carriers: PGT-SR may not always distinguish between a completely normal embryo and one that carries a balanced rearrangement. Some laboratories can identify balanced carriers, but this requires additional analysis and may not be offered routinely.
- Mosaicism: Embryos with a mixture of normal and abnormal cells (mosaicism) can be challenging to interpret. The clinical significance of mosaicism for structural rearrangements is not fully understood.
- No guarantee: PGT-SR reduces but does not eliminate the risk of miscarriage or chromosomal abnormalities. It cannot detect all genetic conditions or guarantee a healthy child.
Need for Prior Genetic Workup
Before undergoing PGT-SR, the carrier parent must have their rearrangement characterized through a karyotype analysis. This information is essential for the laboratory to design the test and interpret results. In some cases, additional testing such as FISH or microarray may be needed to precisely define the breakpoints. Patients should discuss with their genetic counselor or fertility specialist whether their rearrangement is suitable for PGT-SR.
Lab Expertise in Thailand
Thailand has several IVF centers that offer PGT-SR, but the expertise and technology vary. When choosing a clinic, patients should ask about the laboratory’s experience with structural rearrangements, the specific platform used (e.g., NGS, aCGH), and the success rates for similar cases. It is also important to confirm that the lab can perform the necessary validation for the specific rearrangement. Patients may consider consulting with multiple clinics to compare approaches.
Alternatives to PGT-SR
For some couples, alternatives may include:
- Prenatal diagnosis: Chorionic villus sampling (CVS) or amniocentesis during pregnancy to test for unbalanced rearrangements.
- Donor gametes: Using donor eggs or sperm to avoid passing on the rearrangement.
- Natural conception with genetic counseling: Accepting the risk and undergoing prenatal testing if pregnancy occurs.
Each option has its own benefits and limitations, and the choice depends on individual medical history, values, and goals.
Questions to Ask Your Clinic
- What is your experience with PGT-SR for my specific type of rearrangement?
- What technology do you use, and what is its resolution?
- Can you identify balanced carriers, and what is the accuracy?
- What is the cost of PGT-SR, and are there additional fees for carrier testing?
- How many embryos typically survive biopsy and testing?
- What is your policy on mosaic embryos?
Further Reading
For more information, see our guides on PGT in Thailand, patient guides, and frequently asked questions.
Frequently asked questions
Can PGT-SR detect all types of structural rearrangements?
PGT-SR can detect most translocations and inversions, but very small rearrangements may be below the resolution of the test. The laboratory should confirm whether your specific rearrangement is detectable.
Is PGT-SR available in Thailand?
Yes, several IVF centers in Thailand offer PGT-SR. However, the technology and expertise vary, so it is important to discuss with the clinic whether they can test for your specific rearrangement.
Does PGT-SR guarantee a healthy baby?
No. PGT-SR reduces the risk of transferring an embryo with an unbalanced rearrangement, but it does not eliminate all risks of miscarriage, chromosomal abnormalities, or other genetic conditions.
What is the difference between PGT-SR and PGT-A?
PGT-A (aneuploidy testing) screens for extra or missing whole chromosomes, while PGT-SR specifically detects structural rearrangements like translocations and inversions. Some laboratories combine both tests.
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?