At a glance
Embryo grading helps embryologists assess quality before transfer or PGT. Learn how Thai labs grade embryos, what the scores mean, and how to read your report.
What Is Embryo Grading?
Embryo grading is a visual assessment of embryo quality performed by embryologists using a microscope. It does not measure genetic health but helps rank embryos for transfer or biopsy. In Thai IVF labs, grading follows international systems, most commonly the Gardner scale for blastocysts (day 5–6 embryos).
Grading is subjective and varies between labs. Always ask your clinic for a written report and an explanation of their grading criteria.
Why Grading Matters for PGT
Preimplantation genetic testing (PGT) requires a biopsy of several cells from the trophectoderm (future placenta). Embryos with good grades—especially those with a distinct inner cell mass and cohesive trophectoderm—are easier to biopsy and have higher survival rates after biopsy. However, a lower grade does not automatically disqualify an embryo from PGT; the embryologist will decide based on cell number and quality.
PGT results are independent of grade: a top-grade embryo can be abnormal, and a fair-grade embryo can be normal. Grading and PGT are complementary tools.
The Gardner Grading System
The Gardner system evaluates three components of a blastocyst:
- Expansion and hatching status (1–6): 1 = early blastocyst, 2 = blastocyst, 3 = full blastocyst, 4 = expanded blastocyst, 5 = hatching, 6 = hatched.
- Inner cell mass (ICM) quality (A–C): A = many tightly packed cells, B = loosely grouped cells, C = few cells.
- Trophectoderm (TE) quality (A–C): A = many cells forming a cohesive layer, B = fewer cells, C = very few cells.
A typical grade looks like “4AA” (expanded, good ICM, good TE). Some labs add a plus sign (e.g., 4AA+) to indicate slightly better quality.
What the Grades Mean for Transfer
Higher grades (e.g., 4AA, 4AB, 3AA) are associated with higher implantation rates, but many factors affect success, including maternal age, uterine environment, and embryo genetics. A grade B or C embryo can still lead to a healthy pregnancy. Thai labs often freeze embryos of grade 3BB or better, but policies vary—confirm with your clinic.
How to Read Your Embryo Report
Your report will list each embryo with its grade, day of development, and PGT result (if performed). Ask your clinic:
- What grading system do you use?
- What does each letter and number mean?
- Which embryos are considered transferable?
- How does grade affect biopsy success?
Request a copy of the report for your records. If terms are unclear, ask for a plain-language explanation.
Limitations of Grading
Grading is a snapshot of appearance, not function. Two embryos with the same grade can have different genetic or metabolic health. Grading cannot predict implantation with certainty. It is one of several tools used to select embryos.
Questions to Ask Your Thai IVF Lab
- Do you use the Gardner system or another method?
- What is your threshold for freezing or biopsy?
- Can I see time-lapse images or videos of my embryos?
- How do you handle borderline grades?
Being informed helps you participate in decisions. Grading is a guide, not a guarantee.
Frequently asked questions
What is the best embryo grade?
There is no single 'best' grade. In the Gardner system, 4AA or 5AA are considered excellent, but lower grades can still result in healthy pregnancies. Grade is just one factor.
Can a low-grade embryo be used for PGT?
Yes, if the embryo has enough cells for biopsy and survives the procedure. The embryologist will assess each case individually.
Does a high-grade embryo guarantee a normal PGT result?
No. Embryo grade reflects appearance, not genetics. A high-grade embryo can be chromosomally abnormal, and a low-grade embryo can be normal.
How do Thai labs grade embryos?
Most Thai IVF labs use the Gardner system for blastocysts. Some also use time-lapse imaging or AI-assisted grading. Always ask your clinic for their specific criteria.
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.
Need help turning research into a shortlist?
