What is a blastocyst?
A blastocyst is a thin-walled hollow sphere made up of an outer layer of cells that will form the placenta, a fluid filled cavity and an inner cell mass containing cells that will form the embryo. The blastocyst develops after cleavage (e.g. cell division) of the fertilized egg and prior to implantation at approximately five days. Further development occurs only if the blastocyst implants successfully in a uterus. In other words, the blastocyst cannot live on its’ own; it can only become a viable embryo if it is implanted in a woman’s womb.
