At a glance
Understand the differences between PGT-M and PGT-SR, when each is considered, and what to ask a genetic counselor before starting IVF in Thailand.
If you are exploring IVF in Thailand and have a known genetic condition or a chromosomal rearrangement, you may have come across two types of preimplantation genetic testing: PGT-M and PGT-SR. Both are performed on embryos created through IVF, but they look for different kinds of genetic issues. This guide explains the difference in plain English, so you can have more informed conversations with your clinic and a genetic counselor.
At a glance
- PGT-M is used when one or both parents have a specific single-gene disorder (like cystic fibrosis or sickle cell disease).
- PGT-SR is used when a parent has a chromosomal rearrangement (like a translocation) that can lead to embryos with missing or extra chromosomal material.
- Both tests require IVF and embryo biopsy, and neither guarantees a pregnancy or a healthy baby.
- Your genetic counselor and fertility team will help you decide which test, if any, is appropriate for your situation.
What is PGT-M?
PGT-M stands for preimplantation genetic testing for monogenic (single-gene) disorders. It is designed to identify embryos that have inherited a specific genetic condition caused by a change in a single gene. This test is typically considered when one or both partners carry a gene mutation for a condition such as:
- Cystic fibrosis
- Sickle cell disease
- Tay-Sachs disease
- Huntington’s disease
- Thalassemia
PGT-M requires a prior genetic diagnosis in the family. The laboratory needs to know the exact mutation to test for, and often requires blood samples from both parents and sometimes other family members to build a genetic profile.
What is PGT-SR?
PGT-SR stands for preimplantation genetic testing for structural rearrangements. It is used when one parent has a chromosomal rearrangement, such as a balanced translocation or an inversion. These rearrangements usually do not cause health problems in the carrier, but they can lead to embryos with unbalanced chromosomes, which may result in miscarriage, stillbirth, or a child with disabilities.
PGT-SR tests embryos for the correct amount of chromosomal material, aiming to identify embryos that are balanced (like the carrier parent) or completely normal. It does not test for single-gene disorders.
Key differences between PGT-M and PGT-SR
| Aspect | PGT-M | PGT-SR |
|---|---|---|
| Purpose | Detect a specific single-gene disorder | Detect unbalanced chromosomal rearrangements |
| Who might consider it | Couples with a known gene mutation for a monogenic condition | Couples where one partner has a structural chromosomal rearrangement |
| What it looks for | A specific mutation in a single gene | Normal or balanced chromosomal content |
| Prior information needed | Genetic diagnosis of the specific mutation in the family | Chromosomal analysis of the carrier parent |
| Process | IVF, embryo biopsy, DNA analysis for the specific mutation | IVF, embryo biopsy, chromosomal analysis |
How the testing process works
Both PGT-M and PGT-SR are performed as part of an IVF cycle. After eggs are fertilized in the laboratory, embryos are cultured for several days. A small number of cells are then removed from each embryo (a biopsy) and sent to a genetics laboratory for analysis. The results help the fertility team decide which embryos may be suitable for transfer.
The exact steps and timeline can vary between clinics. Your clinic will provide specific instructions and timelines.
When is each test typically discussed?
PGT-M is usually discussed when a couple has a known single-gene disorder in the family and wants to reduce the risk of passing it on. PGT-SR is discussed when a chromosomal rearrangement has been identified in one partner, often after recurrent miscarriages or a previous child with a chromosomal abnormality.
Your doctor or genetic counselor may recommend one test or the other, but the decision is always yours. Some couples may need both PGT-M and PGT-SR if they have both a single-gene disorder and a chromosomal rearrangement, but this is less common.
Questions to ask a genetic counselor
Before deciding on any genetic testing, it is important to speak with a genetic counselor who can explain the risks, benefits, and limitations in your specific situation. Here are some questions you might ask:
- Which test is appropriate for my condition, and why?
- What are the chances that a biopsied embryo will be suitable for transfer?
- What are the limitations of the test? Can it miss anything?
- How long will the testing take, and how will it affect my IVF timeline?
- What are the costs involved, and are there any additional fees for genetic counseling?
- What are the risks of embryo biopsy?
- What are my options if no embryos are suitable for transfer?
Next steps
If you are considering PGT-M or PGT-SR in Thailand, here is a simple checklist to guide you:
- Gather any genetic test results or family history information you have.
- Consult with a genetic counselor to understand your options.
- Choose a fertility clinic that offers the testing you need.
- Ask the clinic about their experience with your specific condition.
- Clarify all costs, timelines, and what happens with the results.
Remember, genetic testing is a personal decision. Take the time you need to feel comfortable with your choices.
Frequently asked questions
Can PGT-M and PGT-SR be done at the same time?
Yes, in some cases both tests can be performed on the same embryo biopsy. This may be recommended if a couple has both a single-gene disorder and a chromosomal rearrangement. However, not all clinics offer combined testing, so you should ask your clinic about their capabilities.
Is PGT-M or PGT-SR guaranteed to prevent a genetic condition?
No. PGT-M and PGT-SR are screening tests that aim to identify embryos with specific genetic issues, but they are not 100% accurate. There is always a small risk of misdiagnosis or that a test may not detect all possible abnormalities. Genetic counseling can help you understand the residual risks.
What is the difference between PGT-A, PGT-M, and PGT-SR?
PGT-A (preimplantation genetic testing for aneuploidy) screens embryos for the correct number of chromosomes. PGT-M tests for a specific single-gene disorder. PGT-SR tests for structural chromosomal rearrangements. They are used for different purposes and can be performed separately or together.
Do I need PGT-M or PGT-SR if I have no known genetic issues?
Not necessarily. PGT-M and PGT-SR are typically recommended only when there is a known genetic risk. Many people do not need these tests. Your doctor or genetic counselor can help you decide based on your medical and family history.
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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