Amniotic Fluid

Amniotic fluid or liquor amnii is the nourishing and protecting liquid contained by the amnion of a pregnant woman. Amnion grows and begins to fill, mainly with water, around two weeks after fertilization. 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.

The amniotic fluid increases in volume as the fetus grows. The amount of amniotic fluid is greatest at about 34 weeks after conception or 34 weeks ga (gestational age). At 34 weeks ga, the amount of amniotic fluid is about 800 ml. This amount reduces to about 600 ml at 40 weeks ga when the baby is born.

Amniotic fluid is continually being swallowed and "inhaled" and replaced through being "exhaled", as well as being urinated by the baby. It is essential that the amniotic fluid be breathed into the lungs by the fetus in order for the lungs to develop normally. Swallowed amniotic fluid contributes to the formation of meconium.

Analysis of amniotic fluid, drawn out of the mother's abdomen in an amniocentesis procedure, can reveal many aspects of the baby's genetic health. This is because the fluid also contains fetal cells which can be examined for genetic defects. 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.

Amniotic fluid also protects the developing baby by cushioning against blows to the mother's abdomen, allows for easier fetal movement, promotes muscular/skeletal development, and helps protect the fetus from heat loss.

The forewaters are released when the amnion ruptures, commonly known as when a woman's "water breaks". When this occurs during labour at term, it is known as "spontaneous rupture of membranes" (SROM). If the rupture precedes labour at term, however, it is referred to as "premature rupture of membranes" (PROM). The majority of the hindwaters remain inside the womb until the baby is born