What is Alpha-Fetoprotein?
Alpha-fetoprotein (AFP) is a protein substance produced by the liver of the fetus. A small amount of this protein is excreted from the kidney of the fetus and passes through the amniotic fluid into the mother's bloodstream. The concentration of AFP in the mother's blood rises gradually into late pregnancy and can be easily measured by a blood test called the maternal-serum-alpha-fetoprotein test, or MSAFP.
When is Testing Done?
The MSAFP is a routine screening blood test for certain fetal disorders and is generally offered to women between the fifteenth and twentieth week of pregnancy. It is most accurate when performed between fifteen and eighteen weeks’ gestation.
What Does This Test Screen For?
Abnormal MSAFP levels are associated with genetic conditions, birth defects, retardation and late-pregnancy complications. Because 70 to 80 percent of all trisomies (a type of inherited genetic defects) occur in women under the age of 35, MSAFP is typically offered to pregnant women of all ages. And, 95 percent of all neural tube defects occur in previously unaffected families.
The AFP Test
Blood can be drawn for this test at the same time as other prenatal tests. Informed consent should be given prior to testing, and a woman has the right to refuse this test if she chooses. If the test reveals abnormal values, a follow-up with an ultrasound and amniocentesis may be recommended for a more definitive diagnosis. Women who have opted for amniocentesis do not need the MSAFP because AFP is included in amniocentesis screening.