Autor NN Team Data: 21.11.2007

What is the amniotic fluid? 

The amniotic fluid is the fluid filling the amniotic sac around the fetus. It has more important functions: 
  • It protects the fetus from trauma (for example, in case of falling down). 
  • It prevents the compression of the umbilical cord which might reduce the oxygen quantity received by the fetus. 
  • It keeps a constant temperature inside the uterus. 
  • It protects the fetus against infections. 
  • It allows the fetus to move so that the muscles and bones develop properly. 
  • It helps the development of the digestive and respiratory systems, because the fetus inhales and exhales, swallows and eliminates amniotic fluid. 
How is the amniotic fluid produced? 

Whithin the 14 weeks of pregnancy, the fluid passes from the circulatory system of mother in the amniotic sac. In the second trimester, the fetus starts swallowing the fluid which passes through the kidneys and is eliminated as urine. Then, he swallows it again, recycling the fluid once at every few hours. (yes, this means a large quantity of the fluid is actually the fetus urine). 

So the fetus has an important role in maintaining the ideal amniotic fluid quantity in the sac. However, this system doesn't work properly sometimes, and the result is a too much or too little quantity of amniotic fluid, both options being dangerous. 

Which is the proper quantity of amniotic fluid? 

Under normal conditions, the quantity of amniotic fluid increases till thebeginning of the last pregnancy trimester. In the 34th week of pregnancythe fluid is at the maximum quantity, almost liter. After this, it decreases until the birth time.

If at some point during the pregnancy the amniotic fluid quantity is too little, the condition is called oligohydramnios. The opposite of this is called polyhydramnios, thus a too much quantity of fluid. About 8% of the pregnant women suffer from oligohydramnios. 

How is the oligohydramnios diagnosed? 

The doctor may suspect this disease if the mother loses amniotic fluid, if her belly is too little for the gestational age or if she doesn't feel the baby's moves. The oligohydramnios may occur in women with low blood pressure, in those who suffer from pre-eclampsia, diabetes or lupus and in those with post-term pregnancy. 

For an exact diagnosis, the doctor recommends an ultrasound to measure the amniotic fluid index (AFI). In the third trimester, the normal index is between 5 and 25 cm. The oligohydramnios diagnosis is established for an index lower than 5 cm. 

Which are the causes of oligohydramnios? 

The doctors don't know all the causes which lead to a low level of amniotic fluid. The disease occurs in the last trimester most frequently, especially if the pregnancy is post-term. Here are some of the most common causes: 

Torn membranes. A small rupture of the membranes allows the fluid to lapse away. This might happen anytime during pregnancy, but most often during the last trimester. The fluid loss may be observed by the mother or by the doctor during the check. A membrane rupture may lead to infections both in the mother and in the fetus, as the bacteria may penetrate the amniotic sac. Sometimes, the ruptures resolve and the amniotic fluid may get back to normal. 

Placenta abnormalities. A placenta abnormality for example a partial detachment, prevents the blood and the nutrients to reach the fetus, thus interrupting the cycle of the amniotic fluid. 

Certain mother diseases. As we mentioned before, certain diseases such as high blood pressure, pre-eclampsia, diabetes and lupus may cause low amniotic fluid levels. 

Fetus abnormalities. If it is noticed that the amniotic fluid is too little during the first or second trimesters of pregnancy, this might be a sign of a fetal defect. Is the fetus doesn't have a kidney or they are poorly developed (Potter syndrome) or has the urinary tract blocked, he cannot produce enough urine to maintain a proper fluid level. 

What happens after the diagnosing? 

A woman who suffers from oligohydramnios will be carefully monitored by her doctor in order to see if the fetus is developing normally. The treatment depends on the gestational age, on the fetus state and on other complications that might exist. No matter the situation, there will be performed periodical ultrasounds to check the fetus state. The mother should drink much water and observe the fetus moves carefully in order to notify the doctor if the fetus is less active. If the pregnancy is close to the term, the birth will be induced not to endanger the fetus health. The oligohydramnios increases the risk of complications at birth. If the fluid level is very low, is possible for the fetus to press on the umbilical cord during the contractions. 

During the labor, the doctor may introduce a warm saline in the uterus sothat the umbilical cord won't be compressed anymore.

Read the English version of this article: Oligohydramnios