All being well, the cells in the blastocyst begin to differentiate.

一切顺利，囊胚中的细胞开始分化。

Common convention is to transfer the embryo three days after fertilization, when the embryo has eight cells, or on day five, when the embryo is called a blastocyst, and has hundreds of cells.

通常的做法是在受精三天后移植胚胎，此时胚胎有八个细胞，或者在第五天移植胚胎， 此时胚胎被称为囊胚，有数百个细胞。