LIFE by Dr. Pat
LIFE by Dr. Pat
Blastocyst grading
How day 5–6 embryos are scored
Author
Dr. Patsama Vichinsartvichai — MClinEmbryol, EFOG-EBCOG, EFRM-EBCOG.
The embryology timeline
| Day | Embryo stage |
|---|---|
| Day 0 | Egg collection and insemination |
| Day 1 | Fertilisation check — two pronuclei (2PN) |
| Day 3 | Cleavage stage, around 8 cells |
| Day 5–6 | Blastocyst stage |
The parts of a blastocyst
- Inner cell mass (ICM) — the cells that become the baby
- Trophectoderm (TE) — the outer cell layer that becomes the placenta
- Blastocoel — the fluid-filled cavity inside the embryo
- Zona pellucida — the clear shell surrounding the embryo
- Perivitelline space — the gap between the shell and the embryo
Expansion status — grades 1 to 6
| Grade | Description |
|---|---|
| 1 | Very early blastocyst |
| 2 | Early blastocyst |
| 3 | Full blastocyst |
| 4 | Expanded blastocyst |
| 5 | Hatching blastocyst |
| 6 | Hatched blastocyst |
Quality of the inner cell mass (ICM) — grades A, B, C
| Grade | Description |
|---|---|
| A | Tightly packed, many cells |
| B | Loosely grouped, several cells |
| C | Very few cells |
Quality of the trophectoderm (TE) — grades A, B, C
| Grade | Description |
|---|---|
| A | Many cells forming a cohesive epithelium |
| B | Few cells forming a loose epithelium |
| C | Very few cells |
Reading a grade — an example
What does grade 4AB mean?
- The 4 — expansion status: an expanded blastocyst
- The first letter A — ICM quality: tightly packed, many cells
- The second letter B — TE quality: few cells forming a loose epithelium
References
- Gardner DK, Lane M, Stevens J, Schoolcraft WB. Blastocyst score affects implantation and pregnancy outcome: towards a single blastocyst transfer. Fertil Steril. 2000;73(6):1155-1158.
- Alpha Scientists in Reproductive Medicine and ESHRE Special Interest Group of Embryology. The Istanbul consensus workshop on embryo assessment: proceedings of an expert meeting. Human Reproduction. 2011;26(6):1270-1283.