The early stage of development is a critical period in the life of a human being. It includes the embryonic and fetal stages, which are characterized by rapid growth and development. The EMBRYO is the first stage of development, which begins after fertilization and lasts until the eighth week of gestation. During this time, the EMBRYO develops all of its major organs and systems. The second stage of development is the fetal stage, which begins at the ninth week of gestation and lasts until birth. During this time, the fetus continues to grow and develop, and its organs and systems become more complex.