The human fetus after 56 days development. The 8th week of pregnancy represents the end of the formative or embryonic stage of development of the ultimate infant. In the preceeding 7 weeks the embryo has grown from a single cell some 0.14 millimeters (mm) in diameter into a complex creature consisting of millions of cells with a length of 30 mm or more. In this early period, organ differentiation (organogenesis) overshadows growth. In the subsequent fetal period, from the 3rd lunar month to birth, the emphasis is on growth rather than differentiation - although the latter continues after birth & in some tissues, throughout life.