Amniotic fluid is a bodily fluid consisting of watery liquid surrounding and cushioning a growing fetus within the amnion. It allows the fetus to move freely without the walls of the uterus being too tight against its body. Buoyancy is also provided. The composition of the fluid changes over the course of gestation. Initially, amniotic fluid is similar to maternal plasma, mainly water with electrolytes. As the fetus develops, proteins, carbohydrates, lipids, phospholipids originating from the lungs, fetal cells, and urea are deposited in the fluid.