What Is PGT and How Does It Work in Thailand IVF?

What Is Preimplantation Genetic Testing (PGT)?

Preimplantation Genetic Testing (PGT) is a set of techniques used during an IVF cycle to examine embryos for genetic or chromosomal conditions before they are transferred to the uterus. The goal is to help select embryos that are more likely to result in a healthy pregnancy. PGT is not a guarantee of a successful pregnancy or a healthy child, and it is not suitable or necessary for everyone.

Types of PGT

There are three main types of PGT, each designed for a different purpose:

PGT-A (Aneuploidy Testing)

PGT-A checks embryos for the correct number of chromosomes. Humans typically have 46 chromosomes (23 pairs). An embryo with too many or too few chromosomes is called aneuploid. Aneuploid embryos often fail to implant or may lead to miscarriage. PGT-A can identify which embryos have the correct number (euploid) and which do not. This can help reduce the risk of miscarriage due to chromosomal abnormalities and may improve the chance of a live birth per transfer, especially for women of advanced maternal age.

PGT-M (Monogenic Disorders)

PGT-M is used when one or both parents carry a known genetic mutation for a specific inherited disorder, such as cystic fibrosis, sickle cell disease, or Huntington’s disease. It tests embryos for that specific mutation to identify which embryos are unaffected. PGT-M requires a custom test to be developed for each family, which takes time and additional cost.

PGT-SR (Structural Rearrangements)

PGT-SR is for individuals who carry a balanced chromosomal rearrangement, such as a translocation or inversion. While the carrier may be healthy, their embryos can have unbalanced chromosomes, leading to implantation failure, miscarriage, or a child with disabilities. PGT-SR identifies embryos with balanced or normal chromosomes.

How Does PGT Work in an IVF Cycle?

The PGT process involves several steps that are integrated into a standard IVF cycle:

1. Ovarian stimulation and egg retrieval: The woman takes medication to stimulate the ovaries to produce multiple eggs. Eggs are collected in a minor surgical procedure.
2. Fertilization: Eggs are fertilized with sperm in the laboratory to create embryos.
3. Embryo culture: Embryos are grown in the lab for about 5–6 days until they reach the blastocyst stage. At this stage, the embryo has two distinct cell types: the inner cell mass (which becomes the fetus) and the trophectoderm (which becomes the placenta).
4. Biopsy: A skilled embryologist uses a laser to make a small hole in the outer shell of the embryo (zona pellucida) and gently removes a few cells from the trophectoderm. The biopsy is performed on day 5 or 6. The embryo is then frozen (vitrified) while the cells are sent for genetic analysis.
5. Genetic analysis: The biopsied cells are analyzed in a genetics laboratory. For PGT-A, techniques like next-generation sequencing (NGS) are commonly used to count chromosomes. For PGT-M and PGT-SR, more specialized methods such as polymerase chain reaction (PCR) or comparative genomic hybridization (aCGH) may be used.
6. Results and embryo selection: Results typically take 1–2 weeks. The report will classify each embryo as euploid (normal), aneuploid (abnormal), or mosaic (a mix of normal and abnormal cells). For PGT-M, embryos are classified as unaffected, affected, or carrier (if applicable). Based on these results, the doctor and patient select one or more embryos for transfer in a subsequent frozen embryo transfer (FET) cycle.

Understanding PGT Results

PGT results are not always straightforward. Here are key terms:

• Euploid: The embryo has the expected number of chromosomes. These embryos have the highest chance of implantation and live birth, but they are not guaranteed to result in a pregnancy or a healthy child.
• Aneuploid: The embryo has missing or extra chromosomes. These embryos are unlikely to implant or will likely miscarry. They are generally not transferred.
• Mosaic: The embryo has both normal and abnormal cells. The clinical significance of mosaicism is still being studied. Some mosaic embryos may still result in a healthy baby, but the risk of abnormalities is higher. Decisions about transferring mosaic embryos should be made with genetic counseling.
• Inconclusive: Sometimes the biopsy sample does not yield enough DNA for analysis, or the result is unclear. In such cases, the embryo may be re-biopsied or discarded depending on clinic policy.

Who Might Consider PGT?

PGT is not for everyone. Common reasons to consider PGT include:

• Advanced maternal age (typically 35 or older)
• Recurrent pregnancy loss
• Repeated IVF failure
• Known chromosomal translocation or inversion in either parent
• Known genetic disorder in the family
• Severe male factor infertility
• Previous child with a chromosomal or genetic condition

However, PGT has limitations and risks. It adds cost to an IVF cycle, requires embryo freezing, and involves a biopsy that, while generally safe, carries a small risk of embryo damage. PGT cannot detect all genetic conditions, and a normal PGT result does not guarantee a healthy baby. Some abnormalities may arise after implantation or be due to factors not tested.

Alternatives to PGT

For some patients, alternatives may be more appropriate:

• No testing: Many couples choose to transfer embryos without PGT, relying on embryo morphology (appearance) and maternal age to select embryos.
• Prenatal testing: After pregnancy is achieved, chorionic villus sampling (CVS) or amniocentesis can diagnose chromosomal or genetic conditions in the fetus.
• Non-invasive prenatal testing (NIPT): A blood test from the mother can screen for common chromosomal abnormalities, but it is a screening test, not diagnostic.
• Donor eggs or sperm: Using gametes from a screened donor can reduce the risk of inherited genetic conditions.

What to Discuss with Your Clinic in Thailand

If you are considering PGT as part of IVF in Thailand, here are important questions to ask your clinic:

• What types of PGT do you offer (PGT-A, PGT-M, PGT-SR)?
• What is the experience of your embryology team with embryo biopsy?
• Which genetic laboratory performs the analysis, and what accreditation do they have?
• How long does it take to receive results?
• What is the policy on mosaic embryos?
• What are the costs for PGT, and what is included?
• What is the success rate for PGT-tested embryos at your clinic? (Note: success rates vary and depend on many factors; ask for their most recent data.)
• Do you offer genetic counseling before and after testing?

PGT is a powerful tool, but it is not a magic solution. Understanding its benefits, limitations, and alternatives will help you make an informed decision in partnership with your fertility team.

Frequently asked questions

What is the difference between PGT-A, PGT-M, and PGT-SR?

PGT-A checks embryos for the correct number of chromosomes (aneuploidy). PGT-M tests for a specific inherited genetic disorder when one or both parents carry a known mutation. PGT-SR is used when a parent has a balanced chromosomal rearrangement, such as a translocation, to identify embryos with normal or balanced chromosomes.

Is PGT necessary for all IVF patients?

No. PGT is not necessary for everyone. It is typically recommended for patients with advanced maternal age, recurrent pregnancy loss, repeated IVF failure, known genetic disorders, or chromosomal rearrangements. Many patients achieve successful pregnancies without PGT.

Does PGT guarantee a healthy baby?

No. PGT reduces the risk of transferring embryos with certain chromosomal or genetic abnormalities, but it cannot detect all possible conditions. A normal PGT result does not guarantee a pregnancy, a live birth, or a child without health issues.

How long does PGT take in an IVF cycle?

After embryo biopsy on day 5 or 6, genetic analysis typically takes 1–2 weeks. Embryos are frozen while waiting for results. The transfer occurs in a subsequent frozen embryo transfer cycle.

What are the risks of embryo biopsy?

The biopsy removes a few cells from the trophectoderm (future placenta). While generally safe, there is a small risk of embryo damage or reduced viability. The long-term effects on the child are considered minimal, but ongoing research continues.

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.