Amniotic fluid

Definition
noun
The protective fluid surrounding the developing fetus within the amniotic sac of a pregnant female
Supplement
The amniotic fluid, also called pregnant female’s water(s) is the fluid surrounding the developing fetus within the amniotic sac. It is said to be protective since it provides an environment that cushions the baby from injury and plays an important role in fetal development. The amniotic fluid is contained within the amniotic sac. It is formed from the maternal plasma and then passes through the fetal membranes. By 16th week of gestational age, the fetus contributes to the amniotic fluid through excreting urine. Thus, the amniotic fluid is initially composed of water and electrolytes and later (about 12th -14th week) it contains proteins, lipids, carbohydrates, phospholipids, and urea.
The volume of the amniotic fluid increases as the fetus develops and grows. In humans, it increases from approximately 25 mL to 400 mL from the 10th week to the 20th week of gestational age. And by the 28th week, it plateaus to 800 mL. At birth, there is about 1L of amniotic fluid.¹ There are certain medical complications involving the amount of amniotic fluid during gestation. When there is not enough amniotic fluid the condition is referred to as oligohydramnios. In contrast, the presence of excess amniotic fluid is referred to as polyhydramnios.
Also called:

• waters
• liquor amnii

See also:

amnion

Related term(s):

• Amniotic fluid embolism
• Amniotic fluid syndrome

Reference(s):

¹ Larsen, W. J. (2001). Human embryology (3. ed.). Philadelphia, Pa.: Churchill Livingstone. p. 490.