Blastocyst Stage (5 days)

Last updated: Jan 31st, 2025

The blastocyst stage occurs approximately five days after fertilization, after the morula has entered the uterine cavity and has developed a fluid-filled cavity. Once the cavity appears, the morula becomes a hollow ball of cells called a blastocyst. Within the blastocyst, cells in one region group together to form an inner cell mass that eventually becomes the embryo.