PGT-A vs PGT-SR: What’s the difference?
PGT-A (preimplantation genetic testing for aneuploidy) and PGT-SR (preimplantation genetic testing for structural rearrangements) are two different types of genetic tests that can be performed on embryos created through IVF. They answer different questions about embryo health.
PGT-A checks embryos for an abnormal number of chromosomes (aneuploidy). This is a common cause of implantation failure and miscarriage. PGT-A is often considered for patients of advanced maternal age, those with recurrent pregnancy loss, or repeated implantation failure.
PGT-SR is specifically designed for patients who carry a structural rearrangement of their chromosomes, such as a translocation or inversion. These rearrangements can lead to embryos with unbalanced chromosomes, which may cause miscarriage or a child with disabilities. PGT-SR aims to identify embryos with a normal or balanced chromosome arrangement.
In Thailand, both tests are available through IVF clinics that offer genetic testing. However, the choice between PGT-A and PGT-SR depends on your specific medical history and genetic situation.
At a glance
- PGT-A: screens for aneuploidy (extra or missing chromosomes).
- PGT-SR: screens for unbalanced structural rearrangements (e.g., translocations).
- Who may need PGT-SR: individuals or couples with a known chromosomal rearrangement.
- Who may need PGT-A: those with age-related risk, recurrent miscarriage, or repeated IVF failure.
- Both tests require IVF and embryo biopsy.
Understanding PGT-A
PGT-A is a screening test that looks for an abnormal number of chromosomes in an embryo. Humans typically have 46 chromosomes, arranged in 23 pairs. An embryo with too many or too few chromosomes is called aneuploid. Most aneuploid embryos fail to implant or result in miscarriage. Some aneuploidies, such as trisomy 21 (Down syndrome), can lead to a live birth with health issues.
PGT-A is often recommended for women over 35, as the risk of aneuploidy increases with maternal age. It may also be suggested for couples who have experienced recurrent pregnancy loss or repeated implantation failure. However, PGT-A does not guarantee a successful pregnancy, and it is not necessary for everyone.
Understanding PGT-SR
PGT-SR is a test for people who carry a structural rearrangement of their chromosomes. Structural rearrangements include translocations (when a piece of one chromosome attaches to another) and inversions (when a chromosome segment is reversed). Carriers often have no health problems themselves, but they may produce embryos with unbalanced chromosomes, leading to miscarriage or a child with disabilities.
PGT-SR is designed to identify embryos that have a normal or balanced chromosome arrangement. This can help reduce the risk of miscarriage and the chance of having a child with a chromosomal disorder. PGT-SR is not a screening test for aneuploidy in general; it is specifically for structural rearrangements.
Key differences between PGT-A and PGT-SR
| Aspect | PGT-A | PGT-SR |
|---|---|---|
| Purpose | Screens for aneuploidy (abnormal number of chromosomes) | Screens for unbalanced structural rearrangements (e.g., translocations) |
| Who it’s for | Patients with age-related risk, recurrent miscarriage, or repeated IVF failure | Patients who carry a known chromosomal rearrangement |
| What it detects | Extra or missing whole chromosomes | Unbalanced chromosome segments due to structural rearrangements |
| Method | Embryo biopsy and genetic analysis (e.g., NGS) | Embryo biopsy and genetic analysis, often with additional testing for the specific rearrangement |
| Outcome | Identifies embryos with normal chromosome number | Identifies embryos with normal or balanced chromosome structure |
When is PGT-SR recommended?
PGT-SR is recommended when one or both partners are known carriers of a structural rearrangement. This is usually identified through a blood test called karyotyping. If you have a history of recurrent miscarriages, a previous child with a chromosomal disorder, or a family history of translocations, your doctor may suggest karyotyping.
If a rearrangement is found, PGT-SR can be used during IVF to select embryos that are less likely to lead to miscarriage or a child with a chromosomal condition. However, PGT-SR is not a guarantee of a healthy baby, and it does not test for all genetic conditions.
PGT-A vs PGT-SR: Which one do you need?
The choice between PGT-A and PGT-SR depends on your medical history and genetic status. If you have a known structural rearrangement, PGT-SR is the appropriate test. If you are considering PGT for age-related aneuploidy or recurrent miscarriage without a known rearrangement, PGT-A may be more relevant.
In some cases, a clinic may recommend both tests, especially if you have a rearrangement and also have age-related aneuploidy risk. However, this is a decision to make with your fertility specialist after a thorough evaluation.
What to ask your clinic in Thailand
If you are considering PGT-A or PGT-SR in Thailand, here are some questions to ask:
- Do you offer PGT-A and PGT-SR? What is the difference in your laboratory?
- How many embryos are typically biopsied, and what is the success rate of the biopsy?
- How long does it take to get results?
- What is the cost of each test, and what does it include?
- Do you have genetic counseling available to help interpret results?
- What are the limitations of the test?
Next steps
If you are trying to decide between PGT-A and PGT-SR, start by reviewing your medical history and any genetic testing you have already had. If you have not had karyotyping, ask your doctor if it is recommended. Then, consult with an IVF clinic in Thailand that offers genetic testing to discuss your options.
Remember, PGT is not a guarantee of pregnancy or a healthy child. It is a tool to help you make informed decisions about which embryos to transfer.
Frequently asked questions
Can PGT-A detect structural rearrangements like translocations?
PGT-A is designed to detect an abnormal number of chromosomes, not structural rearrangements. A structural rearrangement like a translocation may not change the total number of chromosomes, so PGT-A might miss it. PGT-SR is specifically designed to detect unbalanced structural rearrangements.
Is PGT-SR only for people with a known translocation?
Yes, PGT-SR is typically recommended for individuals or couples who are known carriers of a structural rearrangement, such as a translocation or inversion. If you have not been diagnosed with a rearrangement, PGT-SR is unlikely to be offered.
Do I need both PGT-A and PGT-SR?
In some cases, a clinic may recommend both tests, especially if you have a structural rearrangement and also have age-related aneuploidy risk. However, this is not always necessary. Your fertility specialist can advise based on your specific situation.
What is the difference between PGT-SR and PGT-M?
PGT-SR is for structural rearrangements, while PGT-M is for single-gene disorders (like cystic fibrosis or sickle cell anemia). They are different tests for different genetic conditions. Some patients may need both if they have both a rearrangement and a single-gene disorder.
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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.