Amniotic Fluid Analysis

What is an amniotic fluid?

The fluid surrounding the fetus in the amniotic sac is Amniotic fluid. It is derived from maternal plasma in early pregnancy. The fluid volume increases as the baby grows in size.


Functions of the amniotic fluid

1. Provides protection to the fetus.
2. Provides an even temperature.
3. Acts as a cushion to external trauma.
4. Allows the free movement for fetal growth.

Advantages of amniotic fluid analysis

1. Detection of chromosomal abnormalities.
2. Direct measurement of specific enzyme.
3. To detect neural tube defects and lung maturity.

Amniocentesis

Amniocentesis or amniotic fluid analysis is the procedure of removal of small amount of amniotic fluid from amniotic sac. This is done between 16th and 20th week of pregnancy. A needle is inserted into the amniotic sac and 30ml of the fluid is collected. An ultrasonograph guided amniocentesis is done to avoid trauma to the fetus, abortion, infection or respiratory problems.

Amniotic fluid is centrifuged; the supernatant is analyzed for fetal disease. The free floating embryonic cells, which settles at the bottom after centrifugation are tissue cultured. This tissue culture helps to detect the following:

1. The sex of the fetus.
2. Chromosomal disorders.
3. Inherited enzyme deficiency.
4. Rh positive typing.

Investigation using amniotic fluid

Alpha fetoprotein

It is a glycoprotein produced by yolk sac in large amounts in the first trimester and by fetal liver in the second trimester during the intrauterine life.

Pathology
Increase levels of alpha fetoprotein are seen in open neural tube defects like anencephaly, exomphalos and spina bifida. Increased levels are also seen in Turners syndrome.

Creatinine

Creatinine levels are used to detect fetal kidney maturity. If the level of creatinine is less than 2mg/dl this implies renal impairment.

Phospholipids

Dipalmitoyl lecithin and Phosphatidyl inositol appears at 24th week of gestation. It acts as a surfactant without which the lung collapses. Thus the levels of surfactants help to detect fetal lung maturity.

Bile pigments

An increase in bilirubin level helps to detect hemolytic disease of the newborn.

Alkaline phosphatase

An increase in the enzyme level helps in prenatal detection of cystic fibrosis.

Tamm horsfall glycoprotein

This glycoprotein is derived from fetal kidney which acts as an aid to assess renal function.

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