Amniotic fluid

Dr. rer. nat. Daniela Oesterle is a molecular biologist, human geneticist and trained medical editor. As a freelance journalist, she writes texts on health topics for experts and laypeople and edits specialist scientific articles by doctors in German and English. She is responsible for the publication of certified advanced training courses for medical professionals for a renowned publishing house.

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Amniotic fluid surrounds the growing child in the womb almost from the start. It protects against dehydration and external impacts, regulates the temperature in the amniotic sac and, among other things, promotes the development of the child's lungs. The analysis of the color, amount and composition of the liquid provides information about the child's development and possible diseases. Read here, among other things, why green amniotic fluid is a warning label.

Amniotic sac: Protected habitat

The amniotic sac is a sac made of membranes that fills with fluid (amniotic fluid or amniotic fluid) as the child grows. This allows the growing child - only tied to the umbilical cord - to move freely swimming. This enables the child to build up their muscles and skeleton and grow evenly.

In addition, the amniotic fluid takes on a number of other tasks: It prevents the coagulation of the membranes and the embryo, stimulates lung maturation and protects the unborn child from mechanical damage. External shocks, for example, are cushioned, the child remains undamaged by the bulging bladder. In addition, the umbilical cord with its vessels remains free to move and can take care of the child in the best possible way.

The valuable fluid also helps with heat regulation: Development and growth stimulate the child's metabolism enormously. A lot of heat is produced in the process, which the unborn child can give off through the amniotic fluid. This prevents temperature fluctuations, so overheating or hypothermia are not possible.

Shortly before birth, the filled amniotic sac also helps the cervix to open. Before or during childbirth, the amniotic sac bursts (rupture) so that the liquid content flows out.

Formation and composition of amniotic fluid

Amniotic fluid is increasingly formed from around the third week of pregnancy (SSW). It consists of 99 percent water. The rest are made up of proteins, carbohydrates, fats, minerals such as potassium or sodium as well as hormones and skin cells or hairs of the child.

The amniotic fluid is provided on the one hand by the mother and on the other hand by the child. Up to the twelfth week of pregnancy, it essentially originates from the mother by being released through the placenta. In the second half of pregnancy, the child largely takes on the task of production.

Around the 14th week of pregnancy, adolescents begin to drink amniotic fluid. The gastrointestinal tract is stimulated and the amniotic fluid is filtered through the kidneys. From time to time the child empties his bladder, which guarantees a constant exchange of the amniotic fluid. But the child's lungs, the membranes and the placenta also play a role in the exchange. Towards the end of pregnancy, the amniotic fluid is completely renewed approximately every three hours.

Amniotic fluid volume

In the tenth week of pregnancy, the amniotic sac is filled with about 30 milliliters of amniotic fluid. In the 20th week of pregnancy it is already 350 to 500 milliliters. The maximum of 1,000 to 1,200, sometimes even 2,000 milliliters is reached in the 36th week of pregnancy. Then the amount drops to 800 to 1,000 milliliters.

Too much amniotic fluid

In rare cases, the amount of fluid in the amniotic sac is too high. Doctors then speak of polyhydramnios. You can find out more about this in the article Too much amniotic fluid.

Too little amniotic fluid

Sometimes there is also a lack of valuable fluids (oligohydramnios), not because pregnant women lose amniotic fluid, but for other reasons. You can read more about this in the article Too little amniotic fluid.

Determination of the amount of amniotic fluid

The treating doctor uses ultrasound to determine the amount of fluid in the amniotic sac.He must take into account that the amount usually varies from woman to woman and depends on the age of the growing child. So there is no absolute norm. The quantity can be determined in a variety of ways:

Amniotic fluid index

The most common method is to determine the so-called amniotic fluid index (FI). In the ultrasound examination, the abdomen is divided into four quadrants (areas) and the largest amniotic fluid reservoir is determined in each case. The sum of the four measurements gives the FI. In the last trimester of pregnancy, the value is usually between five and eight inches. Values ​​below five centimeters indicate too little, values ​​over 20 centimeters indicate too much amniotic fluid.

Deepest amniotic fluid reservoir

Another possibility is the measurement of the so-called deepest amniotic fluid reservoir. Here the attending physician measures the vertical distance from one side of the membrane to the other. A length of about two to eight centimeters is considered normal. Values ​​below two centimeters indicate too little, values ​​over eight centimeters indicate too much amniotic fluid.

This is the most common measurement method for multiple pregnancies.

Two-diameter amniotic fluid reservoir

With the two-diameter amniotic fluid depot, the horizontal and vertical distance from egg membrane to egg membrane is measured. Vertical and horizontal values ​​are then multiplied. Between about 15 and 50 square centimeters there is nothing to worry about. If the size is less than 15 square centimeters, there is a suspicion of too little amniotic fluid, from 50 square centimeters an excess of the important fluid can be assumed.

Doctor's experience

The experience of the attending physician is not insignificant when determining the quantity. His trained eye is usually enough to recognize deviating amounts of amniotic fluid. Additional results from the ultrasound measurement then enable him to make a reliable statement about the amount of fluid in the amniotic sac.

What does the amniotic fluid look like?

The color of amniotic fluid is in the 15th / 16th centuries. SSW yellowish-clear. Towards the due date, the color changes to whitish-cloudy.

Green amniotic fluid: transmission

Often, when the due date is exceeded, the color of the fluid changes: amniotic fluid can become cloudy due to the first stool excretion of the child (meconium) and take on a green color. The doctor may then decide to initiate the birth. Because if the amniotic fluid mixed with the stool gets into the child's lungs (meconium aspiration), it can sometimes be life-threatening for the newborn. Therefore, the therapeutic suction of the lungs is a first and important medical measure.

Amniotic fluid examination during pregnancy

Pregnant women over 35 years of age are usually offered an amniocentesis (amniocentesis, amniocentesis). The analysis can identify congenital malformations, genetic diseases or infections in the child. Before doing this, the doctor must carefully explain the benefits and possible risks of the procedure to the pregnant woman.

During the procedure, the doctor pierces the pregnant woman's abdominal wall and uterine wall with a fine cannula and sucks off some of the amniotic fluid. This contains cells from children that are examined in the laboratory for genetic defects. Other substances in the liquid also provide information about possible infections or childhood diseases such as an open back.

The amniocentesis is monitored by ultrasound for safety, is hardly painful and usually ends after five to ten minutes. It is usually performed between the 14th and 20th week of pregnancy.

Possible risks

Amniocentesis can cause labor or easy bleeding. The risk of a miscarriage is small at 0.5 to 1 percent. Nevertheless, women should rest for several days after removing amniotic fluid.

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