Amniotic Fluid (Liquor Amnii)

Amniotic fluid, also known as liquor amnii, is a clear, pale-colored fluid in which the fetus floats within the uterus.

Composition and Physical Properties

• Color: Clear, pale-colored.
• Situation: It is present in the amniotic sac from the early weeks of pregnancy (starting around the 13th week) until term.
• Specific Gravity: The specific gravity is 1.000 gm/s.
• pH: The pH is 7.4, indicating it is alkaline in reaction.
• Contents: It contains 99% water, along with mineral salts, 0.25% proteins, urea, hormones, fragments of vernix caseosa, 0.03% glucose, and enzymes.

Sources of Amniotic Fluid

The fluid is generated from several sources:

• Amniotic Membranes: Secreted from the cells of the amniotic membranes.
• Fetal Micturition: The fetus begins to urinate into the fluid, usually from the 16th week of gestation.
• Maternal Vessels: Contributes fluid from maternal vessels from the decidua.
• Fetal Vessels and Placenta: Contributes fluid from fetal vessels and the placenta.

Circulation and Renewal

The fluid is constantly renewed by the swallowing action of the fetus. It is taken in and carried to the placenta through the umbilical cord. At term, 300 milliliters of liquor are changed per hour.

General Functions

Functions During Pregnancy

1. It protects the fetus from external injuries.
2. It allows free movement on the part of the fetus.
3. It maintains the fetus at a constant temperature.
4. It equalizes pressure for the fetus and the cord.
5. It prevents the amnion from sticking onto the fetus and the limbs from sticking together.
6. It provides some nutritive material to the fetus.
7. The fluid distends the amniotic sac and allows the growth and free movement of the fetus.
8. It acts as a shock absorber.
9. It prevents marked interference with fetal circulation.

Functions During Labor

1. By formation of the bag of membranes, it helps to dilate the cervix.
2. It protects the fetus during the first stage of labor from head injuries.
3. It helps to wash out the maternal passage.
4. It aids in the effacement and dilation of the cervix where the presenting part is poorly applied.
5. It helps by its color to determine fetal distress when membranes have ruptured (e.g., meconium staining is denoted as M⁺ or M⁺⁺).
6. During labor, it protects the placenta and cord from the pressure of uterine contractions as long as the membranes remain intact.

Abnormalities in Volume

Polyhydramnios (Hydramnios)

This is an excessive amniotic fluid volume of 1500 milliliters or more.

Causes of Polyhydramnios

• Maternal Diabetes: Poorly controlled blood glucose levels.
• Congenital Abnormalities of the Fetus: For instance, esophageal atresia (inability to swallow the fluid).
• Twin Pregnancy: Can occur in cases where there are two amniotic membranes.
• Infection: Infection of the amniotic membrane can lead to excessive excretion.

Dangers of Polyhydramnios

• The umbilical cord is likely to prolapse when the membranes rupture due to the sudden release of fluid.

Oligohydramnios

This is the condition in which there is a reduced volume of amniotic fluid, which can be as little as 300 milliliters or even less.

• Impact: It does not allow for free fetal movement, which can lead to a Talipes baby (clubfoot) due to over-squeezing during intrauterine life.

Causes of Oligohydramnios

1. Inactive Amniotic Membrane: The amniotic membrane is inactive or fails to secrete sufficient fluid.
2. Infection: Infection of the amniotic membrane.

Abnormalities in Color

Deviation from the normal clear color is an important fetal distress indicator and has clinical significance.

• Meconium Stained (Green): Suggestive of fetal distress in presentations other than breech or transverse. Depending upon the degree and duration of the distress, it may be thin or thick or pea soup (thick with flakes). Thick fluid with the presence of flakes suggests chronic fetal distress.
• Golden Color: Occurs in Rh incompatibility due to excessive hemolysis of the fetal red blood cells (RBCs) and the production of excess bilirubin.
• Greenish Yellow (Saffron): Suggestive of post-maturity.
• Dark Colored: Found in concealed accidental hemorrhage due to contamination of blood.
• Dark Brown (Tobacco Juice): Found in Intrauterine Death (IUD). The dark color is due to the frequent presence of old HbA (Hemoglobin A) products.