At a glance
Understand the differences between PGT-A, PGT-M, and PGT-SR, who each test is for, and how to decide which one fits your IVF journey in Thailand.
What Is Preimplantation Genetic Testing (PGT)?
Preimplantation genetic testing (PGT) is a set of techniques used during an IVF cycle to examine embryos for specific genetic or chromosomal features before transfer. PGT is not a single test — it includes several types, each designed for a different purpose. Understanding the difference between PGT-A, PGT-M, and PGT-SR can help you have a more informed conversation with your fertility specialist.
It is important to know that PGT does not guarantee a pregnancy, a healthy baby, or eliminate all risks. It is a screening or diagnostic tool that provides information to help guide embryo selection. Not every IVF patient needs PGT, and the decision should be based on your medical history, age, and family planning goals.
PGT-A: Aneuploidy Screening for Chromosome Number
What It Does
PGT-A (preimplantation genetic testing for aneuploidy) checks embryos for the correct number of chromosomes. A normal human cell should have 46 chromosomes (23 pairs). An embryo with too many or too few chromosomes is called aneuploid. Most aneuploid embryos will not implant, or if they do, they may result in miscarriage or conditions such as Down syndrome (trisomy 21).
Who Might Consider PGT-A
- Women of advanced maternal age (typically 35 and older), as the chance of producing aneuploid eggs increases with age.
- Couples with recurrent pregnancy loss where chromosomal abnormalities may be a contributing factor.
- Couples with repeated IVF failure despite having good-quality embryos.
- Anyone who wants to reduce the risk of transferring an aneuploid embryo, though it does not eliminate all risks.
Limitations
- PGT-A cannot detect all genetic disorders; it only looks at chromosome number and large structural rearrangements.
- There is a small chance of a false positive or false negative result due to mosaicism (a mix of normal and abnormal cells in the embryo) or technical limitations.
- PGT-A does not guarantee implantation or a live birth.
PGT-M: Testing for Single-Gene Disorders
What It Does
PGT-M (preimplantation genetic testing for monogenic disorders) looks for specific inherited genetic conditions caused by a mutation in a single gene. Examples include cystic fibrosis, sickle cell disease, Huntington’s disease, and many others. PGT-M requires a custom test to be developed for each family, based on the known mutation(s).
Who Might Consider PGT-M
- Couples who are carriers of a known genetic disorder and want to avoid passing it to their children.
- Individuals with a family history of a single-gene condition who have been tested and found to carry the mutation.
- Couples who have had a previous child affected by a genetic disorder and wish to prevent recurrence.
Limitations
- PGT-M requires prior genetic testing of the parents to identify the specific mutation. A custom probe or test must be designed, which can take weeks to months.
- It only tests for the specific condition(s) requested; it does not screen for all genetic disorders or chromosomal abnormalities.
- PGT-M is not available for every genetic condition; feasibility depends on the mutation and laboratory capabilities.
PGT-SR: Testing for Chromosomal Structural Rearrangements
What It Does
PGT-SR (preimplantation genetic testing for structural rearrangements) is used when one or both parents carry a balanced chromosomal rearrangement, such as a translocation or inversion. These rearrangements do not usually cause health problems in the carrier, but they can lead to embryos with unbalanced chromosomes, increasing the risk of miscarriage or birth defects.
Who Might Consider PGT-SR
- Individuals known to carry a balanced translocation or inversion (often identified through karyotype testing).
- Couples with a history of recurrent miscarriage where a parental chromosomal rearrangement is suspected or confirmed.
- Couples with a previous child born with a chromosomal structural abnormality.
Limitations
- PGT-SR cannot correct the rearrangement; it only identifies embryos with a normal or balanced chromosomal structure.
- Some embryos may be identified as abnormal even if they are balanced carriers (like the parent), which are generally healthy. The test may not always distinguish between a normal and a balanced carrier, depending on the technique used.
How to Decide Which Test You Need
The choice between PGT-A, PGT-M, and PGT-SR depends on your specific medical and genetic situation. Here are some common scenarios:
- Scenario 1: You are over 35 and concerned about age-related chromosomal abnormalities. PGT-A may be recommended to screen embryos for aneuploidy.
- Scenario 2: You and your partner are carriers of a genetic disorder like cystic fibrosis. PGT-M would be the appropriate test, often combined with PGT-A if you also want chromosome screening.
- Scenario 3: You have a balanced translocation and have experienced miscarriages. PGT-SR is designed for this situation, and it may be combined with PGT-A.
- Scenario 4: You have no known genetic or chromosomal issues but want to maximize the chance of a healthy baby. PGT-A may be an option, but it is not medically necessary for everyone. Discuss the pros and cons with your doctor.
In many cases, PGT-A is performed alongside PGT-M or PGT-SR as an add-on to also check chromosome number. Your fertility clinic and genetic counselor can help you determine the best approach.
What to Discuss with Your Fertility Specialist
Before deciding on PGT, ask your doctor these questions:
- Based on my age, medical history, and family history, which PGT test is most appropriate for me?
- What are the success rates and limitations of the recommended test at your clinic?
- How many embryos are typically needed to have a reasonable chance of finding a suitable embryo for transfer?
- What is the timeline for testing, and how long will it take to get results?
- What are the costs involved, and are there any additional fees for combined testing?
PGT in Thailand: What You Should Know
Thailand has several fertility centers that offer PGT services. When researching clinics, consider the following:
- Laboratory accreditation: Look for clinics with international certifications such as JCI, ISO, or CAP, which indicate quality standards.
- Genetic counseling: Ensure the clinic provides or can refer you to a genetic counselor who can explain test results and implications.
- Experience with your specific test: Ask how many PGT-M or PGT-SR cycles the lab has performed for your condition.
For a list of fertility centers in Thailand that offer PGT, visit our PGT in Thailand page. You can also explore our guides and FAQ for more information.
Important Reminders
- PGT is not a guarantee of a healthy baby. It reduces but does not eliminate the risk of genetic or chromosomal conditions.
- Not all embryos will be suitable for testing or transfer. Some embryos may not survive the biopsy process.
- PGT results should always be interpreted by a qualified genetic counselor or reproductive specialist.
Frequently asked questions
Can I have both PGT-A and PGT-M in the same IVF cycle?
Yes, it is common to combine PGT-A with PGT-M or PGT-SR. The same embryo biopsy sample can be used for multiple tests. However, this may increase the time required for analysis and the overall cost. Discuss with your clinic whether combined testing is available and appropriate for your situation.
Does PGT guarantee that my baby will be healthy?
No. PGT screens for specific chromosomal or genetic conditions, but it cannot detect all possible disorders. There is also a small risk of misdiagnosis. A healthy embryo identified by PGT can still have other health issues not related to the tested conditions.
Is PGT necessary for all IVF patients?
No. PGT is not medically necessary for everyone. It is typically recommended for patients with specific risk factors, such as advanced maternal age, known genetic disorders, or recurrent pregnancy loss. Your fertility specialist can help you decide if PGT is right for you.
How long does PGT take?
PGT-A results are usually available within a few days to two weeks after embryo biopsy. PGT-M and PGT-SR may take longer because they require custom test development, which can add several weeks to the overall timeline. Ask your clinic for an estimated timeline.
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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