Embryo grading decoder
Enter or pick a grade like 4AB, or a day-3 cleavage grade, and see a plain-language, illustrated decode of what each part means — and just as importantly, what a grade can't tell you.
Which grade do you have?
Expansion (1–6)
Inner cell mass (A–C)
Trophectoderm (A–C)
Grade 4AB
Illustrative diagram, not to scale — a stylised drawing, not a photograph of an embryo.
Expanded blastocyst
Expanded blastocyst — large cavity, the outer shell (zona) is thinning. A common stage to transfer or freeze.
Inner cell mass (ICM) — becomes the baby
Tightly packed, many cells — the top grade.
Trophectoderm (TE) — becomes the placenta
Fewer cells, a looser lining.
Reaching blastocyst by day 5 is, on average, a slightly better sign than reaching it on day 6 — but good day-6 blastocysts succeed all the time.
What the grading shorthand means
This tool turns a grade your clinic reads out over the phone into something you can see and understand. Day 5–6 blastocyst grades like 4AB have three parts (expansion, inner cell mass, trophectoderm); day-3 cleavage-stage grades describe cell number and fragmentation. For the full explainer, see embryo grading explained, and what it can't tell you.
Default grade: 4AB
Illustrative diagram, not to scale — a stylised drawing, not a photograph of an embryo.
Day 5–6 — expansion (the number)
| Value | Meaning | |
|---|---|---|
| 1 — Early blastocyst | Early blastocyst — the fluid cavity is just starting to form. | |
| 2 — Blastocyst | Blastocyst — the cavity fills about half the embryo. | |
| 3 — Full blastocyst | Full blastocyst — the cavity fills the embryo. | |
| 4 — Expanded blastocyst | Expanded blastocyst — large cavity, the outer shell (zona) is thinning. A common stage to transfer or freeze. | |
| 5 — Hatching blastocyst | Hatching blastocyst — the embryo is starting to break out of its shell. | |
| 6 — Hatched blastocyst | Hatched blastocyst — the embryo has fully escaped its shell. |
Reaching blastocyst by day 5 is, on average, a slightly better sign than reaching it on day 6 — but good day-6 blastocysts succeed all the time.
Day 5–6 — inner cell mass (first letter · becomes the baby)
| Value | Meaning | |
|---|---|---|
| A | Tightly packed, many cells — the top grade. | |
| B | Loosely grouped, fewer cells. | |
| C | Very few, sparse cells. |
Day 5–6 — trophectoderm (second letter · becomes the placenta)
| Value | Meaning | |
|---|---|---|
| A | Many even cells forming a neat lining — the top grade. | |
| B | Fewer cells, a looser lining. | |
| C | Few large or uneven cells. |
Day 3 — cell number
Around 6 to 8 cells is typical for a good day-3 embryo; fewer or many more can be normal too. A day-3 grade is a snapshot of an early moment and tells you much less than what the embryo does by day 5 — which is why many clinics grow embryos on to day 5 before deciding.
Day 3 — fragmentation / evenness
| Value | Meaning | |
|---|---|---|
| Even, little fragmentation | Clean, evenly sized cells — the better-looking end. | |
| Some fragmentation | A moderate amount of cell debris; still commonly transferred. | |
| More fragmentation / uneven | More debris or uneven cells; on its own not a verdict — day-3 looks change fast. |