embryonic stem cell

Embryonic stem cells (ES cells) are pluripotent stem cells derived from the inner cell mass of the blastocyst, an early-stage embryo.[1] Human embryos reach the blastocyst stage 4–5 days post fertilization, at which time they consist of 50–150 cells. Because isolating the embryoblast or inner cell mass (ICM) results in the death of the fertilized human embryo, this raises ethical issues.