Estriol is produced mostly in the placenta and in the liver of the fetus. Estriol levels are lower than normal in most pregnancies with a fetus with Down syndrome. A triple screen test is also performed at 15-20 weeks of pregnancy. As in the AFP test, a small amount of blood is taken from a vein in the woman's arm. Usually the same blood sample is used for all the tests.
Results are usually available within a week.
Maternal serum screening tests, such as the alpha-fetoprotein test and the multiple marker screening test, assess your risk of having a baby with a birth defect. This is possible because the amniotic fluid contains cells from the fetus that have the same genetic makeup as the fetus. A small amount of this fluid is taken from the sac surrounding the fetus and tested. You may be offered amniocentesis if your chances are higher than normal for having a baby with a birth defect that the test can detect well. Finally . . .