What is a blastocyst?
A blastocyst is a cluster of cells made by a fertilized egg. It contains the very early stages of an embryo. A blastocyst is the first phase for the fertilized egg that will lead to a pregnancy.
A blastocyst forms about five to six days after a sperm has fertilized an egg. Cells in the blastocyst divide and separate. These cells eventually become both the protection and nourishment for the developing fetus.
The blastocyst stage of a fertilized egg is especially important in vitro fertilization (IVF). Around day five, the blastocyst is graded by the embryologist at your IVF clinic, assigned a "grade" and the determination is made if it will be transferred, frozen or discarded based around the "grade" assigned and your situation.
A blastocyst contains two distinct features:
- Trophectoderm / T cells.
- Single layer of cells around the outside of the embryo that will become the placenta and embryonic sac.
- Inner Cell Mass (ICM)
- Cluster of cells that will form the fetus.
References