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Human embryonic stem cells originate from the human preimplantation embryo. Stem cells derived from the inner cell mass of blastocyst, an early stage of preimplantation embryo, 4 days after fertilization are called embryonic stem cell. Embryonic cells can give rise to every cell type in the fully formed body, but not the placenta and umbilical cord. They have the capacity to differentiate into cellular derivatives of the endodermal, ectodermal, and mesodermal lineages. Most embryonic stem cells are developed from eggs that have been fertilized in an in-vitro clinic, not from eggs fertilized in-vivo.