Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Amniotic fluid is the 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 amnion grows and begins to fill, mainly with water, around two weeks after fertilisation. After a further 10 weeks the liquid contains proteins, carbohydrates, lipids and phospholipids, urea and electrolytes, all which aid in the growth of the fetus. In the late stages of gestation much of the amniotic fluid consists of fetal urine.
Recent research by researchers led by Anthony Atala of Wake Forest University and a team from Harvard University has found that amniotic fluid is also a plentiful source of non-embryonic stem cells. These cells have demonstrated the ability to differentiate into a number of different cell-types, including brain, liver and bone.
The forewaters are released when the amnion ruptures, commonly known as when a woman's "water breaks" or "spontaneous rupture of membranes" (SROM). The majority of the hindwaters remain inside the womb until the baby is born.
Too little amniotic fluid (oligohydramnios) or too much (polyhydramnios or hydramnios) can be a cause or an indicator of problems for the mother and baby. In both cases the majority of pregnancies proceed normally and the baby is born healthy but this isn't always the case. Babies with too little amniotic fluid can develop contractures of the limbs, clubbing of the feet and hands, and also develop a life threatening condition called hypoplastic lungs. If a baby is born with hypoplastic lungs, which are small underdeveloped lungs, this condition is potentially fatal and the baby can die shortly after birth.
On every prenatal visit, the obstetrician/gynaecologist should measure the patient's fundal height with a tape measure. It is important that the fundal height be measured and properly recorded to insure proper fetal growth and the increasing development of amniotic fluid. The obstetrician/gynaecologist should also routinely ultrasound the patient—this procedure will also give an indication of proper fetal growth and amniotic fluid development. Oligohydramnios can be caused by infection, kidney dysfunction or malformation (since much of the late amniotic fluid volume is urine), procedures such as chorionic villus sampling (CVS), and preterm premature rupture of membranes (PPROM).
Oligohydramnios can sometimes be treated with bed rest, oral and intravenous hydration, antibiotics, steroids, and amnioinfusion.
Polyhydramnios is a predisposing risk factor for cord prolapse and is sometimes a side effect of a macrosomic pregnancy. Hydramnios is associated with esophageal atresia. Amniotic fluid is primarily produced by the mother until 16 weeks of gestation.
Preterm premature rupture of membranes (PPROM) is a condition where the amniotic sac leaks fluid before 38 weeks of gestation. This can be caused by a bacterial infection or by a defect in the structure of the amniotic sac, uterus, or cervix. In some cases, the leak can spontaneously heal, but in most cases of PPROM, labor begins within 48 hours of membrane rupture. When this occurs, it is necessary that the mother receive treatment to avoid possible infection in the newborn.
A rare and often fatal obstetric complication is an amniotic fluid embolism, which causes disseminated intravascular coagulation.