How Many Embryos Are Typically Biopsied for PGT in Thailand?

When planning preimplantation genetic testing (PGT) in Thailand, one of the most common questions is how many embryos will be available for biopsy. The answer varies because it depends on several factors, including your age, ovarian reserve, and how many eggs are retrieved and fertilized. In general, only embryos that reach the blastocyst stage (day 5 or 6 of development) are suitable for biopsy. This means the number biopsied is always a subset of the total embryos created in a cycle.

This article explains typical biopsy numbers, the risk of embryo loss during the process, and how these factors affect your cycle planning. Since exact numbers depend on individual circumstances, we focus on what you can expect and what questions to ask your clinic.

At a Glance: Key Points About PGT Biopsy Numbers

• Biopsy is performed on blastocyst-stage embryos (day 5–6).
• Not all fertilized eggs reach the blastocyst stage; attrition is normal.
• Typically, 40–60% of fertilized eggs may become blastocysts, but this varies widely.
• Only good-quality blastocysts are biopsied; poor-quality ones may not be suitable.
• Biopsy itself carries a small risk of embryo damage (estimated <5% in experienced labs).
• Freezing after biopsy (vitrification) has high survival rates (>90% in reputable clinics).
• Final biopsy numbers depend on your individual cycle and clinic protocols.

What Determines How Many Embryos Are Biopsied?

The number of embryos biopsied for PGT is not a fixed figure. It is the result of a cascade of steps, each with its own attrition rate. Understanding this cascade helps set realistic expectations.

1. Number of Eggs Retrieved and Fertilized

Your age and ovarian reserve largely determine how many eggs are retrieved after ovarian stimulation. On average, 8–15 mature eggs are retrieved per cycle, but this can range from a few to over 20. Of those, about 70–80% fertilize via ICSI (intracytoplasmic sperm injection), which is standard for PGT to avoid sperm DNA contamination.

2. Embryo Development to Blastocyst

Not all fertilized eggs develop into blastocysts. Embryo attrition is a natural process: some embryos arrest at earlier stages. Typically, 40–60% of fertilized eggs reach the blastocyst stage by day 5 or 6. This percentage can be lower for older women or those with certain fertility diagnoses.

3. Embryo Quality and Suitability for Biopsy

Only blastocysts of sufficient quality are biopsied. Clinics grade embryos based on expansion, inner cell mass, and trophectoderm quality. Poor-grade blastocysts may not be suitable for biopsy or may have lower survival rates after the procedure. Your embryologist will select the best-quality blastocysts for biopsy.

4. Clinic Policies and Laboratory Expertise

Different clinics may have slightly different criteria for which embryos to biopsy. Some may biopsy all blastocysts, while others only biopsy those with good or fair quality. The skill of the embryology team also affects how many embryos survive the biopsy and freezing process.

What Is the Risk of Embryo Loss During Biopsy?

Biopsy involves removing a few cells from the trophectoderm (the outer layer that becomes the placenta). This is a delicate procedure, and there is a small risk of damaging the embryo. In experienced laboratories, the risk of embryo loss due to biopsy is estimated to be less than 5%. Most embryos that survive biopsy also survive the subsequent vitrification (freezing) process, with survival rates above 90% in reputable clinics.

It is important to note that some embryos may not be suitable for biopsy at all, and others may not survive the thaw after genetic testing. These losses are part of the PGT process and should be discussed with your doctor when planning your cycle.

How Biopsy Numbers Affect Cycle Planning

Knowing that not all embryos will be biopsied helps you plan your PGT cycle realistically. Here are key considerations:

• Multiple cycles may be needed: If you produce few blastocysts, you may need more than one egg retrieval to have enough embryos for testing and transfer.
• Genetic testing results reduce numbers further: After biopsy, PGT-A (aneuploidy testing) typically shows that 30–70% of blastocysts are chromosomally normal, depending on maternal age. For PGT-M (monogenic disorders), the chance of an unaffected embryo depends on the inheritance pattern.
• Plan for attrition: A realistic expectation is that from 10 fertilized eggs, you might get 4–6 blastocysts, of which 3–5 are biopsied, and 1–3 may be genetically normal. These numbers are illustrative and vary.
• Discuss with your clinic: Ask your clinic for their specific data on blastocyst formation rates, biopsy survival rates, and genetic abnormality rates for patients similar to you.

Questions to Ask Your Clinic About Biopsy Numbers

To get a clearer picture of what to expect, consider asking your clinic these questions:

• What is your average blastocyst formation rate for patients in my age group?
• What percentage of blastocysts are typically suitable for biopsy?
• What is your embryo survival rate after biopsy and vitrification?
• How many embryos do patients like me typically have available for transfer after PGT?
• Do you biopsy all blastocysts or only those of a certain grade?

Next Steps: Planning Your PGT Cycle

Understanding biopsy numbers is just one part of PGT planning. Here is a checklist to help you move forward:

• Consult with a fertility specialist to assess your ovarian reserve and discuss stimulation protocols.
• Ask about the clinic’s experience with PGT and their laboratory success rates.
• Discuss the costs of PGT, including biopsy, genetic testing, and embryo freezing.
• Consider whether you need PGT-A, PGT-M, or PGT-SR based on your medical history.
• Plan for the possibility of multiple cycles if you have a low ovarian reserve or specific genetic needs.

For more detailed information, explore our guides on PGT in Thailand and fertility treatment guides, or check our FAQ section for common questions.

Frequently asked questions

How many embryos are typically biopsied in one PGT cycle?

There is no fixed number because it depends on how many eggs are retrieved, fertilized, and develop into good-quality blastocysts. On average, from 10–15 eggs, you might get 3–6 blastocysts suitable for biopsy, but this varies widely by age and individual factors.

What percentage of embryos survive the biopsy process?

In experienced laboratories, over 95% of biopsied embryos survive the procedure. The risk of embryo loss due to biopsy is small, typically less than 5%.

Can all blastocysts be biopsied?

Not always. Only blastocysts of sufficient quality (usually grade B or better) are biopsied. Poor-quality blastocysts may not survive the procedure or may not yield enough cells for testing.

Does PGT increase the risk of losing embryos?

PGT involves a small additional risk of embryo damage from biopsy and freezing. However, in skilled hands, the overall survival rate is high. The main loss occurs naturally during embryo development, not from the testing itself.

How many embryos will be genetically normal after PGT?

The proportion of normal embryos depends on maternal age and the specific genetic test. For PGT-A, about 30–70% of blastocysts may be euploid (normal), with younger women having higher rates. For PGT-M, the chance of an unaffected embryo depends on the inheritance pattern.

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.