At a glance
PGT-A screens embryos for abnormal chromosome numbers, while PGT-SR checks for unbalanced structural rearrangements. Learn what each test does, when it might be used, and questions to ask your clinic.
PGT-A vs PGT-SR: What’s the Difference?
If you are exploring IVF with genetic testing, you may have come across terms like PGT-A and PGT-SR. Both are types of preimplantation genetic testing (PGT) performed on embryos before transfer, but they look for different kinds of genetic issues. PGT-A (aneuploidy screening) checks for abnormal numbers of chromosomes, while PGT-SR (structural rearrangement testing) looks for unbalanced rearrangements of chromosome segments. Understanding the difference can help you have a more informed conversation with your fertility specialist.
At a Glance: PGT-A vs PGT-SR
- PGT-A screens for aneuploidy – missing or extra whole chromosomes.
- PGT-SR detects unbalanced structural rearrangements – when parts of chromosomes are swapped, deleted, or duplicated.
- Both tests require IVF and biopsy of embryos.
- Neither test can guarantee a healthy baby or eliminate all genetic risks.
What Is PGT-A?
PGT-A, previously known as preimplantation genetic screening (PGS), is designed to identify embryos with an abnormal number of chromosomes. Humans typically have 46 chromosomes – 23 from each parent. Aneuploidy occurs when an embryo has extra or missing chromosomes, which can lead to implantation failure, miscarriage, or conditions such as Down syndrome (trisomy 21).
PGT-A is often considered for patients who are older, have experienced recurrent miscarriage, or have had multiple failed IVF cycles. However, it is not a routine requirement for everyone, and its benefit depends on individual circumstances.
What Is PGT-SR?
PGT-SR is used when one or both partners carry a structural chromosomal rearrangement, such as a balanced translocation or inversion. These rearrangements usually do not affect the carrier’s health, but they can lead to embryos with unbalanced genetic material, increasing the risk of miscarriage or a child with disabilities.
PGT-SR identifies embryos that have inherited a balanced set of chromosomes, similar to the carrier parent, or a completely normal set. This can help reduce the chance of transferring an embryo with unbalanced rearrangements.
Key Differences Between PGT-A and PGT-SR
| Aspect | PGT-A | PGT-SR |
|---|---|---|
| What it tests | Number of chromosomes (aneuploidy) | Structural rearrangements (unbalanced) |
| Who might consider it | Patients with advanced maternal age, recurrent miscarriage, or repeated implantation failure | Couples where one partner carries a balanced translocation or inversion |
| How it works | Biopsied cells are analyzed for chromosome copy number | Biopsied cells are analyzed for chromosomal structure and balance |
| Limitations | Cannot detect all genetic abnormalities; may not improve live birth rates for all patients | Cannot detect all structural rearrangements; may not eliminate all risks |
When Might PGT-A or PGT-SR Be Recommended?
Your doctor may suggest PGT-A if you have specific risk factors for aneuploidy. PGT-SR is typically recommended when a chromosomal rearrangement is known in either partner. However, the decision to use either test should be based on your medical history, family planning goals, and a thorough discussion with your fertility team.
It is important to note that neither test is mandatory for all IVF patients. Some people may choose not to test, and others may opt for alternative approaches such as prenatal testing during pregnancy.
Limitations and Considerations
Both PGT-A and PGT-SR have limitations. They require a biopsy of the embryo, which is an invasive step, though risks are generally low. The tests are highly accurate but not perfect – there is a small chance of a false result. Also, these tests cannot detect all genetic conditions, such as single-gene disorders (which would require PGT-M).
Furthermore, having a “normal” result does not guarantee a successful pregnancy or a healthy baby. Many factors contribute to IVF success, including embryo quality, uterine environment, and overall health.
Questions to Ask Your Clinic
- Why do you recommend PGT-A or PGT-SR for my situation?
- What are the risks and benefits of the test?
- How many embryos are typically biopsied, and what is the likelihood of having no embryos to transfer?
- What is the accuracy rate of the test at your lab?
- Are there alternative options, such as prenatal testing?
Next Steps
If you are considering PGT, start by discussing your medical history and family-building goals with a fertility specialist. They can help you understand whether PGT-A, PGT-SR, or another type of testing might be appropriate. You can also explore our PGT in Thailand guide and other guides for more information. For general questions, visit our FAQ page.
Frequently asked questions
Can PGT-A and PGT-SR be done at the same time?
Yes, in some cases both tests can be performed on the same embryo biopsy. However, the decision depends on your specific genetic situation and the laboratory’s capabilities. Your clinic can advise whether combined testing is appropriate for you.
Does PGT-A improve the chance of having a baby?
PGT-A may reduce the risk of transferring an embryo with an abnormal number of chromosomes, which could lower the chance of miscarriage. However, it does not guarantee a live birth, and its overall benefit varies by patient. Discuss your individual prognosis with your doctor.
Is PGT-SR only for people with a known chromosomal rearrangement?
Typically, yes. PGT-SR is most useful when one partner is known to carry a balanced translocation or inversion. Without such a finding, PGT-SR is unlikely to be recommended.
Are there risks to the embryo from biopsy?
Embryo biopsy is generally considered safe, but it is an invasive procedure. There is a small risk of damage to the embryo, though this is rare. Your clinic will explain the specific risks and benefits in your case.
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.
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