Introduction
The amniotic fluid is the clear liquid that is found in the amniotic sac of a pregnant woman, where it helps to protect the embryo or fetus. At an early stage of embryonic development, two separate cavities are created: the amniotic cavity and the chorionic cavity. From the 3rd month, these two cavities merge with each other, the amniotic cavity develops into the amniotic sac and the chorionic cavity into the placenta. In the course of time, the amniotic cavity steadily increases in volume at the expense of the chorionic cavity. The amniotic fluid contained in it is largely formed by the epithelial cells of the amniotic cavity (i.e. fetal tissue), which surround the entire amniotic sac.
Components
The amniotic fluid consists of both maternal and embryonic parts. The maternal components enter the amniotic sac via the blood through the placenta, the embryo releases fluid mainly in the form of urine and also via the skin, lungs and umbilical cord into the amniotic fluid. Apart from water, the amniotic fluid is composed of various electrolytes (including sodium and potassium), proteins, lactate, urea, glucose and also some exfoliated epithelial cells of the embryo.
Determination of the amniotic fluid
With the help of an ultrasound, the amniotic fluid index can be used to determine the amount of amniotic fluid present, which should be done at every preventive examination during pregnancy. The standard values are about 30ml in the 10th week of pregnancy, about 400ml in the 20th week of pregnancy and about 1 liter shortly before birth. Especially in children who are born late, the amount of amniotic fluid can decrease again towards the end of the pregnancy.
The existing amniotic fluid is not the same water from the beginning to the end of the pregnancy. It is subject to a cycle which ensures that the amniotic fluid is completely replaced within 3 hours. The production and absorption of amniotic fluid should therefore be in balance during a regular pregnancy. The child drinks from the amniotic fluid, which is then absorbed through the intestines and enters the mother’s bloodstream via the placenta and is then excreted into the amniotic sac via the kidneys.
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