A sample of the mother's blood is taken to measure the amount of a special protein produced by the fetus. Too much or too little of the protein indicates that the genes may not be working right. Therefore, the brain or spine of the fetus may not be developing properly. In such cases, other prenatal tests can be done to confirm any problem. Other prenatal tests check fetal cells to see if important enzymes are present.
Enzymes are proteins that trigger activity in the cells of the body.
Some diseases are caused when the gene that gives the instructions for producing an enzyme doesn't work. When that happens, the enzyme is not produced, and an important function of the body does not occur. This leads to the disease. A particular enzyme test is usually done only when the fetus is at risk for the related disease, for example, if the disease runs in the family. Another common prenatal test is ultrasound imaging .