The amniotic fluid, in which the fetus is suspended in during pregnancy, is situated between the two fetal membranes, the amnion and the chorion. This fluid is a clear, water-like fluid which appears around the 7th week of pregnancy and is filtered out of the maternal blood via the amniotic epithelium into the amniotic cavity.
The interior of the amniotic sac is filled with this fluid, which creates the proper environment in the womb, allowing the fetus to move freely and creating a shock- absorbent barrier protecting the fetus from mechanical injury. The fluid also protects the fetus from drying out, and from temperature fluctuations, and it also enables metabolism of the fetus to allow the transport of nutrients. At first it is mainly water with electrolytes, but around the 12-14th week the fluid also contains proteins, carbohydrates, lipids, phospholipids, and urea, which supports the growth of the fetus.
The amniotic fluid contains many cell types (i.e., amniocytes) that arise from the developing fetus (derived from the skin, the digestive tract of the developing embryo/fetus, and from the amniotic membrane). Amniotic fluid is obtained from week 14 until the end of the pregnancy. The composition and origin of cells in the amniotic fluid vary as the pregnancy progresses, yielding a heterogeneous population.
Both the amniotic membrane and the amniotic fluid contain cells that may be of therapeutic interest.