| Table 1. Gardner and Schoolcraft Classification System (Gardner et al., 2000; 2004) |
| Size and expansion |
| Classification |
Description |
| 1 |
Early blastocyst: the blastocele is less than half the volume of the embryo |
| 2 |
Blastocyst: the blastocele is greater than or equal to half of the volume of the embryo. |
| 3 |
Full blastocyst: the blastocele completely fills the embryo. |
| 4 |
Expanded blastocyst: the blastocele volume is larger than that of the early embryo and the zona pellucida is thinning. |
| 5 |
Hatching blastocyst: the trophectoderm has started to herniate through the zona pellucida. |
| 6 |
Hatched blastocyst: the blastocyst has completely escaped from the zona pellucida. |
| ICM (Inner Cell mass) |
| Classification |
Description |
| A |
tightly packed, many cells |
| B |
loosely grouped, several cells |
| C |
very few cells |
| Trophectoderm (TE) |
| Classification |
Description |
| A |
many cells forming a tightly knit epithelium |
| B |
few cells |
| C |
very few cells forming a loose epithelium |
| (Balaban et al., 2006). |