Embryo grading explained
A plain-English guide to embryo grading, blastocyst grades, lab updates, and the questions worth asking before transfer.
Prepared by Embrilia. Educational, source-linked, and designed to help you prepare for a conversation with your care team.
Key takeaways
- Embryo grading describes appearance and development under the microscope.
- Clinics use different grading systems, so ask your lab how it reports grades.
- A grade can support selection, but it cannot reliably predict live birth by itself.
Medical note
This guide is for education and appointment preparation. It is not medical advice, diagnosis, or a substitute for your fertility clinic's instructions.
What embryo grading is
Embryo grading is the lab's way of describing how an embryo looks and develops at a certain point in time. It is usually based on cell number, cell appearance, development speed, and, for blastocysts, the appearance of the inner cell mass and trophectoderm.
The grade helps the embryology team decide which embryo may be best suited for transfer or freezing. It is not a promise. Age, genetics, uterine factors, transfer technique, clinic protocols, and plain biology all matter too.
Day 3 versus blastocyst grading
On day 3, embryos are often called cleavage-stage embryos. Labs commonly look at the number of cells, whether cells are similar in size, and whether there is fragmentation.
On day 5, 6, or sometimes 7, an embryo may reach the blastocyst stage. Blastocyst grading often uses a number for expansion plus letters for the inner cell mass and trophectoderm. For example, in a grade such as 4AA, the number describes expansion, the first letter describes the inner cell mass, and the second letter describes the trophectoderm.
What the letters and numbers can mean
A higher-looking grade often means the embryo had reassuring visual features at the time it was checked. The inner cell mass is the group of cells associated with the future fetus, while the trophectoderm is associated with the future placenta.
Different labs may define and report grades differently. A grade from one clinic is not always directly comparable to the same-looking grade from another clinic. Ask your embryologist or fertility doctor to translate your report using your clinic's system.
| Part of grade | What it usually describes | Question to ask |
|---|---|---|
| Expansion number | How expanded the blastocyst appears | Was the embryo fully expanded, hatching, or still developing? |
| Inner cell mass letter | Appearance of cells associated with the future fetus | How does this lab define A, B, and C? |
| Trophectoderm letter | Appearance of cells associated with the future placenta | How much does this factor influence transfer priority? |
| Day reached | Whether the embryo became a blastocyst on day 5, 6, or 7 | Does timing change how you rank or freeze embryos? |
How grading differs from genetic testing
Grading looks at appearance. PGT-A looks at the number of chromosomes in sampled embryo cells. They answer different questions, and neither one can guarantee an outcome.
Some embryos with strong visual grades may have abnormal chromosome results, while some lower-looking grades may still lead to pregnancy. If your clinic recommends PGT-A, ask what it may and may not tell you for your age, history, and number of embryos.
Questions for your embryology update
Embryology calls can arrive when you are anxious and distracted. Write down your questions before the call, and ask for spelling or a portal message if you are unsure what you heard.
- How many eggs were mature, and how many fertilized normally?
- How many embryos are still developing today?
- Which grading system does this clinic use?
- Which embryos are recommended for transfer, freezing, biopsy, or continued culture?
- What would make the plan change tomorrow?
FAQ
Does an AA embryo always work?
No. A strong grade is encouraging, but embryo grading cannot reliably predict live birth on its own. It is one part of a larger clinical picture.
Is a day 6 blastocyst bad?
Not necessarily. Many clinics freeze and transfer day 6 blastocysts. Ask your clinic how it weighs blastocyst day, grade, genetic testing, and your medical history.
Is embryo grading the same as PGT-A?
No. Grading describes appearance under the microscope. PGT-A tests sampled cells for chromosome number and is a separate decision with its own limits.