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Amniotic fluid surrounds the embryo and fetus during development and has a myriad of functions. Physically, it protects the fetus in the event the maternal abdomen is the object of trauma. Furthermore, it protects the umbilical cord by providing a cushion between the fetus and the umbilical cord, thus reducing the risk of compression between the fetus and the uterine wall.[1] Amniotic fluid also helps protect the fetus from infectious agents due to its inherent antibacterial properties. Additionally, it serves as a reservoir of fluid and nutrients for the fetus containing: proteins, electrolytes, immunoglobulins, and vitamins from the mother. It provides the necessary fluid, space, and growth factors to allow normal development and growth of fetal organs such as the musculoskeletal system, gastrointestinal system, and pulmonary system.[2]  Clinicians can use amniotic fluid as a tool to monitor the progression of pregnancy and predict fetal outcomes.

Homeostasis of body fluids is important in the growing fetus. In addition to the constant circulation of amniotic fluid through inhalation and exhalation, there must be a balance between fluid formation and elimination.[4] The formation originates from fetal urine and lung secretions; however, elimination which is important for balance and homeostasis, is largely the result of fetal swallowing and intramembranous absorption.[7][8] Early in pregnancy, embryonic skin is just simple epithelium, allowing fluid to pass freely under hydrostatic and osmotic forces.[3] Furthermore, its composition is similar to the fetus and maternal serum; it freely diffuses through fetal skin and the chorionic villi until week 8. Eventually, fetal skin begins to become stratified epithelium and becomes fully keratinized by 25 weeks.[4][9] Once the skin of the fetus is fully keratinized later in pregnancy, it can no longer absorb or transfer fluids as easily back and forth. Respiration, swallowing, and urination are the main routes of exchange between the fetus and amniotic fluid to maintain the fluid balance.[3] The two largest contributors to elimination are fetal swallowing and the intramembranous pathway. Though there are many mechanisms for eliminating amniotic fluid, the greatest contributor to amniotic fluid elimination is through fetal swallowing, seen as early as 11 weeks.[10][11]