Fetus development occurs between the embryonic stage of development and birth in humans. This stage begins after 11 weeks of gestation, when the embryo begins to exhibit human characteristics, and lasts until birth. Typically, all the major organs and tissues can be observed; however, they are not yet fully developed or appropriately situated within the body.
Throughout the process of fetal development, the growing fetus goes through three distinct stages, each characterized by specific events.
2 ¼ to 4 months
As the embryo enters the fetal stage of development, the placenta becomes functional. The fetus typically measures 30 mm from the crown to the rump and weighs approximately 8 g (shown below). By the end of this stage, the fetus is approximately 15 cm. During this time, several organs can be observed, including the hands, feet, heart, and brain. The pancreas and liver begin to secrete fluids. In addition, the genitals begin form and the head is prominent, comprising almost half of the fetal body. The fetus also exhibits unregulated movements required for the lung, muscle, and neurological development that is occurring.