Difference Between Amniotic Fluid and Urine

Amniotic Fluid vs Urine

Amniotic fluid and urine are two important fluids in the animal body. They serve many functions in the body. However, the main component of these two fluids is water. The anatomy and physiology of urine and amniotic fluid vary widely.

Amniotic Fluid

Amniotic fluid is a colorless fluid that is found inside a membranous sac, called amnion and formed from the placenta. It is the fluid that surrounds the developing fetus and mainly consists water. It also contains protein, sugar, sodium chloride, sodium, non-protein nitrogen, creatinineurea and uric acid. In addition, it allows the fetus to move freely in the placenta and maintains even temperature condition around fetus.

The basic functions of amniotic fluid are to serve as a cushion and protect the fetus from vibrations, and exchange of substances such as water and molecules between the fetus and maternal circulation. Amniotic fluid has a much similar composition of maternal plasma. The quantity of amniotic fluid increases steadily throughout the pregnant period, and it reaches up to 1100-1500 mL by the 36th week of gestation. Then the amount starts to reduce to about 400 mL at the 42nd week. The quantity of fluid is examined ultrasonically by measuring amniotic pockets.


The liquid nitrogenous waste, which is produced and excreted by the urinary system of animals, is called urine. It is produced in the kidney and drains through ureters into the urinary bladder, where it is stored temporary until urination takes place. Urinary bladder can usually hold 150-500 mL of urine before pain receptors are initiated.

Urine is mainly composed of about 95% of water and 5 % of urea, which is the waste resulted due to the breakdown of proteins. However, in some cases, if a person has high blood glucose, the excess glucose is expelled with urine. Remarkably, it is found that no bacteria found in urine, unless the urinary system has no infection, and thus urine is quite sterile, unlike feces. Urine may also contain ions such as K+, H+.

Urine is important to maintain the acid-base balance of blood because of their high H+. In addition, amount of water in urine allows maintaining the blood volume and pressure.

What is the difference between Amniotic Fluid and Urine?

• Urine is a nitrogenous waste, unlike the amniotic fluid.

• Amniotic fluid is colorless fluid. In contrast urine may contain pigments which give it pale yellow color.

• Amniotic fluid is present only during the pregnancy, whereas urine is present throughout the lifetime.

• Amniotic fluid is derived from the placenta, whereas urine is formed by kidney.

• Amniotic fluid is important to keep the fetus in the body, whereas urine is important to balance the acid-base level, blood volume and pressure.

• Amniotic fluid is expelled through the vagina during the delivery of child, whereas urine is expelled through urethra.

• Amniotic fluid is stored inside the uterus, whereas urine is stored in the urinary bladder.

• Amniotic fluid amount can reach up to the maximum level of 1100-1500 mL, whereas the maximum amount of urine that a human can store is 150-500 mL.


Read more:

1. Difference Between Discharge and Amniotic Fluid

2. Difference Between Mucus Plug and Water Breaking