| Table 2. Veeck and Zaninovic Classification System |
| Blastocyst ≥50% cavity/Cavitated morula <50% cavity |
| Classification |
Description |
| Degree of expansion and hatching status |
| 1 |
Early blastocyst; the blastocoel filling more than half the volume of the conceptus, but no expansion in overall size as compared to earlier stages |
| 2 |
Blastocyst; the blastocoel filling more than half of the volume of the conceptus; with slight expansion in overall size and notable thinning of the zona pellucida. |
| 3 |
Full blastocyst; a blastocoel of more than 50% of the conceptus volume and overall size fully enlarged with a very thin zona pellucida |
| 4 |
Hatching blastocyst; non-preimplantation genetic diagnosis. The trophectoderm has started to herniate through the zona |
| 5 |
Fully hatched blastocyst; non-preimplantation genetic diagnosis. Free blastocyst fully removed from zona pellucida |
| 6 |
Hatching or hatched blastocyst; preimplantation genetic diagnosis |
| Inner cell mass (ICM) |
| A |
Tightly packed, compacted cells |
| B |
Larger, loose cells |
| C |
No ICM distinguishable |
| D |
Cells if ICM appear degenerative |
| Trophectoderm (TE) |
| A |
Many healthy cells forming a cohesive epithelium |
| B |
Few, but healthy large cells |
| C |
Poor, very large, or unevenly distributed cells, may appear as few cells squeezed to the side |
| D |
Cells of the trophectoderm appear degenerative |
| (Veeck & Zaninovic, 2003). |