PGT-A vs PGT-M vs PGT-SR in Thailand: Which Test Do You Need?

What Is Preimplantation Genetic Testing (PGT)?

Preimplantation genetic testing (PGT) is a set of techniques used to analyze embryos created through in vitro fertilization (IVF) before they are transferred to the uterus. PGT helps identify embryos with certain genetic characteristics, allowing patients and doctors to make more informed decisions about which embryo to transfer. It is important to understand that PGT does not guarantee a pregnancy, a healthy baby, or eliminate all risks of genetic disorders. The decision to use PGT should be made after thorough counseling with a fertility specialist and a genetic counselor.

There are three main types of PGT: PGT-A, PGT-M, and PGT-SR. Each screens for different genetic features, and the choice depends on your medical history, age, and specific concerns.

PGT-A (Aneuploidy Screening)

What It Screens For

PGT-A checks embryos for the correct number of chromosomes. Humans typically have 46 chromosomes (23 pairs). An embryo with an abnormal number of chromosomes is called aneuploid. Aneuploidy is a common cause of implantation failure, miscarriage, and certain genetic conditions such as Down syndrome (trisomy 21).

Who Might Consider PGT-A

• Women of advanced maternal age (typically over 35), as the risk of aneuploidy increases with age.
• Couples with a history of recurrent miscarriage, which may be due to chromosomal abnormalities.
• Couples with repeated IVF implantation failure.
• Individuals with a known chromosomal abnormality in themselves or a previous child.

How It Is Performed

During an IVF cycle, embryos are cultured to the blastocyst stage (day 5 or 6). A few cells are biopsied from the trophectoderm (the part that becomes the placenta). The cells are then sent to a genetics laboratory for analysis, typically using next-generation sequencing (NGS). Results usually take 1–2 weeks, and embryos are frozen while waiting for results.

Limitations

• PGT-A cannot detect all genetic disorders, only large chromosomal gains or losses.
• There is a small risk of misdiagnosis due to mosaicism (a mix of normal and abnormal cells in the embryo).
• Some embryos classified as abnormal may self-correct or be viable, leading to unnecessary discard.
• PGT-A does not improve the chance of pregnancy for all patients; its benefit is most clear for specific groups.

PGT-M (Monogenic Disorder Screening)

What It Screens For

PGT-M is designed to detect specific single-gene disorders (monogenic diseases) such as cystic fibrosis, sickle cell anemia, Huntington’s disease, or thalassemia. It is used when one or both parents are known carriers of a genetic mutation that could cause a serious condition in their child.

Who Might Consider PGT-M

• Couples where one or both partners have a known genetic mutation for an autosomal dominant or recessive disorder.
• Couples who have had a previous child affected by a monogenic disease.
• Individuals with a family history of a specific genetic condition.

How It Is Performed

PGT-M requires a customized test for each family. Before the IVF cycle, the genetics lab needs DNA samples from the parents and sometimes an affected family member to design a test that identifies the specific mutation. This process can take several weeks to months. During IVF, embryos are biopsied similarly to PGT-A, and the cells are analyzed for the specific mutation. PGT-M is often combined with PGT-A to also screen for aneuploidy.

Limitations

• PGT-M only screens for the specific mutation(s) requested; it does not check for other genetic conditions.
• Test development is time-consuming and may not be available for very rare mutations.
• There is a small risk of misdiagnosis due to technical errors or recombination.
• PGT-M cannot guarantee that the child will be free from the condition; confirmatory prenatal testing is often recommended.

PGT-SR (Structural Rearrangement Screening)

What It Screens For

PGT-SR is used when one parent carries a balanced chromosomal rearrangement, such as a translocation (where pieces of chromosomes have swapped places) or an inversion (a segment of a chromosome is reversed). These rearrangements are usually harmless to the carrier but can lead to unbalanced chromosomes in embryos, causing miscarriage or birth defects.

Who Might Consider PGT-SR

• Individuals or couples where one partner has a known balanced translocation or inversion.
• Couples with a history of recurrent miscarriage or infertility due to a chromosomal rearrangement.

How It Is Performed

PGT-SR uses similar biopsy and analysis techniques as PGT-A, but the genetic analysis focuses on detecting unbalanced rearrangements. Often, the same NGS platform can be used, but the interpretation requires expertise in structural variants. PGT-SR can also be combined with PGT-A to screen for aneuploidy.

Limitations

• PGT-SR cannot detect all types of rearrangements; some may be too small to identify.
• It may not be able to distinguish between balanced carriers and completely normal embryos, which is important for the child’s future fertility.
• As with other PGT types, there is a risk of misdiagnosis and no guarantee of a healthy outcome.

How PGT Is Performed in Thailand

Thailand has several IVF centers that offer PGT services. The process generally follows international standards:

1. IVF Cycle: Ovarian stimulation, egg retrieval, fertilization (usually via ICSI), and embryo culture to blastocyst stage.
2. Embryo Biopsy: A few cells are removed from the trophectoderm on day 5 or 6. The biopsy is performed by an experienced embryologist.
3. Genetic Analysis: The biopsied cells are sent to an on-site or partner genetics laboratory. Most Thai labs use NGS for PGT-A and PGT-SR, and PCR-based methods for PGT-M.
4. Embryo Freezing: Embryos are vitrified (frozen) while awaiting results, which typically take 1–2 weeks.
5. Transfer: A frozen embryo transfer (FET) is scheduled in a subsequent cycle, using a chromosomally normal (euploid) embryo if available.

It is important to confirm with your chosen clinic whether they have an in-house genetics lab or work with an external laboratory, as this can affect turnaround time and logistics.

Which Test Do You Need?

The choice between PGT-A, PGT-M, and PGT-SR depends on your specific situation:

Test	Recommended For	Example Scenario
PGT-A	Patients concerned about age-related aneuploidy, recurrent miscarriage, or repeated IVF failure	A 38-year-old woman with no known genetic disorders but worried about chromosomal abnormalities
PGT-M	Couples known to carry a specific single-gene disorder	Both partners are carriers of cystic fibrosis and want to avoid having an affected child
PGT-SR	Individuals with a balanced translocation or inversion	A man with a balanced translocation who has experienced recurrent miscarriages with his partner

Some patients may benefit from a combination of tests. For example, a couple undergoing PGT-M may also opt for PGT-A to screen for aneuploidy. Your fertility doctor and genetic counselor will help you decide based on your medical history, family history, and personal preferences.

Alternatives and Important Considerations

• No PGT: Many patients choose to transfer embryos without genetic testing. This is a valid option, especially for younger women with no known genetic risks.
• Prenatal Testing: After pregnancy is achieved, prenatal screening (e.g., NIPT, amniocentesis) can provide additional information about the fetus.
• Donor Eggs or Sperm: For patients with a high risk of genetic disorders, using donor gametes may be an alternative.
• Cost and Time: PGT adds significant cost and time to an IVF cycle. Confirm all fees and timelines with your clinic.
• Legal and Ethical Aspects: Regulations regarding PGT vary by country. In Thailand, PGT is permitted for medical reasons, but sex selection for non-medical reasons is prohibited. Always verify current laws with your clinic.

Questions to Ask Your Clinic

• What types of PGT do you offer? Are they performed in-house or sent to an external lab?
• What is the success rate for embryo biopsy and survival after thawing?
• How long does it take to get results?
• What is the cost of each PGT type, and what does it include?
• Do you offer genetic counseling before and after testing?
• What happens if no euploid embryos are available for transfer?

Conclusion

PGT-A, PGT-M, and PGT-SR are powerful tools that can help select embryos with a lower risk of certain genetic conditions. However, they are not guarantees and come with limitations. In Thailand, these tests are available at many IVF centers, but the specific protocols and costs vary. Work closely with your medical team to understand which test, if any, is right for you.

For more information, see our PGT in Thailand overview, guides, and FAQ.

Frequently asked questions

Can I have both PGT-A and PGT-M done on the same embryo?

Yes, it is possible to combine PGT-A and PGT-M in a single biopsy. The same few cells can be used for both aneuploidy screening and mutation detection. This is often done when a couple has a known monogenic disorder and also wants to screen for chromosomal abnormalities. However, not all labs offer combined testing, so confirm with your clinic.

Is PGT mandatory for IVF in Thailand?

No, PGT is not mandatory for IVF in Thailand. It is an optional procedure that patients may choose based on their medical history and preferences. Many patients undergo IVF without any genetic testing.

How accurate is PGT?

PGT is highly accurate but not 100%. The accuracy depends on the type of test, the laboratory's expertise, and the quality of the biopsy. For PGT-A, the error rate is generally low (around 1-2%), but mosaicism can lead to ambiguous results. For PGT-M, the risk of misdiagnosis is typically less than 1% when the test is properly designed. Confirmatory prenatal testing is often recommended after pregnancy.

Does PGT increase the chance of a live birth?

PGT-A may improve the chance of live birth per transfer in certain groups, such as women over 35, by selecting euploid embryos. However, it does not increase the overall chance of pregnancy per IVF cycle because some embryos may be discarded. For PGT-M and PGT-SR, the primary goal is to avoid transferring affected embryos, not necessarily to improve live birth rates. The impact on live birth varies by individual circumstance.

Continue your research

• PGT in Thailand overview
• PGT and IVF guides
• Frequently asked questions

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.