A fœtus is the developmental stage of a human or animal that occurs after the embryonic stage and before birth. In humans, this stage typically begins around the 8th week of pregnancy and lasts until birth. During this time, the fœtus undergoes significant growth and development, including the formation of organs, limbs, and other body structures. The fœtus is surrounded by amniotic fluid within the amniotic sac, which provides protection and allows for movement. Nutrients and oxygen are supplied to the fœtus through the placenta, an organ that connects the developing baby to the mother's blood supply. This stage is crucial for the proper development of the baby before it is born.