Embryo grades explained gives you a way to read IVF reports and understand how clinics describe embryo quality.
Staring at an IVF embryo report can feel like reading shorthand only the lab understands. Codes such as “3BB” or “grade 2, eight cells” sit next to your name and raise fair questions about what that means for your cycle.
This article explains embryo grading in straightforward everyday terms. You will see how clinics score embryos on different days, what the letters and numbers stand for, and where grading fits into wider treatment decisions. The aim is not to promise a result, but to help you follow the conversation and ask clear questions.
Embryo Grades Explained In Plain Language
Embryo grading is a visual scoring system. At set points after fertilisation, an embryologist views each embryo through the microscope and records what it looks like. The result is a code that sums up cell number, shape, and structure at that moment.
Grading mainly reflects appearance. It does not measure chromosomes directly or guarantee a pregnancy from any single embryo. Modern grading systems build on criteria agreed by professional groups so that labs can speak in a shared way about embryo development. One example is the updated ESHRE oocyte and embryo morphology assessment guideline, which sets out timing and structural features that clinics record.
On day 3, embryos are still dividing into separate cells. Scores centre on cell number, how even those cells look, and how many tiny fragments sit between them. By day 5 or 6, grading shifts from simple counts to blastocyst structure.
| Grading Term | What The Lab Checks | What The Grade Suggests |
|---|---|---|
| Cell Number (Day 3) | Total cells on day 3. | Six to ten cells fits expected timing. |
| Fragmentation | Tiny pieces of cell material between main cells. | Less fragmentation often links with steadier growth. |
| Cell Symmetry | How similar the cells look. | Even cells suggest smoother early growth. |
| Blastocyst Expansion | Size of the inner fluid cavity. | Higher numbers show later blastocyst stage. |
| Inner Cell Mass Grade | Cluster that later forms the baby. | Letter grade reflects how compact and full it looks. |
| Trophectoderm Grade | Outer cell layer that forms the placenta. | Letter grade reflects how even and crowded that layer looks. |
| Overall Score Or Band | Single summary word or number. | Helps rank embryos in one cycle. |
| Prenamed Scales | Simple labels such as “good,” “fair,” or “poor.” | Groups embryos into broad bands for quick sorting. |
When you hear a team member talk about a “grade 1 cleavage embryo” or a “5AA blastocyst,” they are using short labels for these checks. Exact wording can shift between clinics, yet the basic building blocks stay similar. The early grades describe cell number and shape, while later grades describe blastocyst structure.
Embryo Grading Explained For Day 3 And Day 5 Embryos
Embryos change fast in the first week, so labs adapt their grading systems as the embryo grows. A day 3 grade does not use the same logic as a blastocyst code. Knowing which day the grade belongs to is the first step to reading it correctly.
How Day 3 Cleavage Embryos Are Graded
On day 3 after egg retrieval, many embryos sit between six and ten cells. The embryologist counts the cells and checks how evenly they share space inside the shell. A common pattern gives the cell number first and then a score or short word that describes appearance.
Two features drive most day 3 scores: timing and fragmentation. An embryo with eight even cells and little debris usually sits near the top of the list. One with fewer cells or many fragments may receive a lower score. Some clinics grade from 1 to 4 or 1 to 5, while others use words such as “good,” “fair,” and “poor”.
How Day 5 Blastocyst Embryos Are Graded
By day 5 or 6, many embryos have moved past simple cell counts and into the blastocyst stage. The most widely used grading system at this point uses a number followed by two letters, such as 3BB or 5AA.
The number often runs from 1 to 6 and refers to expansion. Lower numbers tend to mark early blastocysts with a small fluid cavity. Middle numbers show a cavity that fills most of the shell. The highest numbers usually belong to embryos where the shell has stretched so much that it begins to thin or crack.
The first letter scores the inner cell mass, the tight cluster that later forms the fetus. A often points to many compact cells, B to a looser group, and C to a sparse or uneven cluster. The second letter scores the trophectoderm, the ring that later forms the placenta, and follows the same A through C idea.
With this system, a 5AA blastocyst often sits near the top of the list for transfer or freezing, while a 3BC may sit lower. That pattern shows how clinics rank embryos, not how your story will unfold. Many people have children from lower grade embryos, and no grading sheet can predict the course of one cycle with total accuracy.
How Embryo Grades Show Up On IVF Reports
Once you know the basic grading pieces, the lines on a clinic portal or printed report start to look clearer. Reports usually list embryo ID numbers, day of development, stage, and grade. Short notes or plus symbols may sit beside the main code for extra detail.
A sample entry might read “Embryo 3: day 5, 4AB, frozen.” Here the number 3 marks the internal ID tag and day 5 shows when grading took place. The 4AB code signals a fully expanded blastocyst with a strong inner cell mass and a slightly less even trophectoderm. The word frozen means the lab chose to store that embryo for a later transfer.
| Sample Report Line | Plain Language Meaning | Helpful Question To Ask |
|---|---|---|
| “Day 3, 8 cells, grade 1” | Eight even cells with little fragmentation. | How does this score compare with your clinic’s best day 3 embryos? |
| “Day 3, 5 cells, grade 3” | Embryo behind expected timing on day 3. | Can this embryo catch up, or is that unlikely at your centre? |
| “Day 5, 3BB blastocyst” | Early blastocyst with middle letter grades. | Would the team transfer this embryo now or wait another day? |
| “Day 5, 5AA blastocyst” | Expanded blastocyst with high letter grades. | Is this a leading choice for single embryo transfer in your clinic? |
| “Day 6, 4BC blastocyst, frozen” | Day 6 blastocyst with mixed letters that still met freezing cut off. | What results does the clinic usually see with embryos in this range? |
| “Grade: good, fair, poor” | Shorthand scale that groups embryos into three bands. | How do these words map onto the number and letter grades you use? |
| “No embryos suitable to freeze” | No embryo met the lab cut off for storage. | Which features does the lab expect before it will freeze an embryo? |
Each clinic builds its own reporting style. Some units list only simple words, while others include exact expansion numbers, letter grades, and photos. If any code still feels unclear, you can bring a copy of the report to your next appointment and ask your team to walk through it with you.
What Embryo Grades Mean For IVF Success Chances
Many people look for a chart that links each grade to a specific pregnancy rate. Research shows that higher grade embryos tend to implant more often than lower grade embryos, but the ranges overlap. A 4BB blastocyst can lead to a baby while a 5AA blastocyst from the same cycle may not.
Professional groups describe grading as one decision tool among many. Age, egg source, sperm quality, previous treatment history, uterine findings, and genetic testing all sit alongside the lab score. The 2025 ESHRE and ALPHA Istanbul consensus update notes that grading captures structure and timing but cannot show every factor that matters for implantation.
Embryo grades also interact with the number of embryos transferred in each cycle. For people with several strong blastocysts, many clinics now recommend single embryo transfer to lower twin rates and risks linked with multiple pregnancy. Guidance such as the ESHRE guideline on the number of embryos to transfer encourages clinics to weigh embryo quality alongside age and medical history.
Genetic testing, when used, adds another layer. A lower grade embryo that tests chromosomally normal may offer a stronger chance than a higher grade embryo that tests abnormal. In cycles that use testing, the genetic result usually guides decisions more than small differences between letter grades.
How To Talk About Embryo Grades With Your Clinic Team
Once you have embryo grades explained in language that makes sense, you can turn that knowledge into practical questions. Bringing a printed report or screenshot to each visit helps you follow along as the doctor or embryologist runs through each embryo.
You can ask which grading system your clinic uses and what each part of the code means there. An “A” at one centre may not match an “A” across town. Ask which embryos the team would pick for transfer and why, whether they would suggest single or double transfer, and what they expect from any frozen embryos.
It also helps to share how much detail you prefer. Some people feel calmer hearing every score; others prefer a short summary and a clear simple plan. Tell your team what works for you so they can match their explanations to your needs.
Most of all, try to treat embryo grades as one source of information, not a verdict on your cycle or your chances as a whole. Grading helps doctors and embryologists sort options, but it does not define you or your hopes for a family.