Table 1.

Expansion Grading of Blastocyst

Expansion grade	Blastocyst development and stage status
1	Early blastocyst: the blastocoel is less than half the volume of the embryo
2	Blastocyst: the blastocoel is greater than or equal to half of the volume of the embryo
3	Full blastocyst: the blastocoel completely fills the embryo
4	Expanded blastocyst: the blastocoel 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 zona pellucida
6	Hatched blastocyst: the blastocyst has completely escaped from the zona pellucida