α-fetoprotein (AFP) is a major plasma protein produced by the yolk sac and the liver during fetal development. Plasma levels decrease rapidly after birth but begin decreasing prenatally starting at the end of the first trimester. Normal adult levels are usually achieved by the age of 8 to 12 months. AFP is measured in pregnant women through the analysis of maternal blood or amniotic fluid, as a screening test for a subset of developmental abnormalities. AFP will be elevated in some of the diseases, including omphalocele, hepatocellular carcinoma/hepatoma, neural tube defects, nonseminomatous germ cell tumors, yolk sac tumor, ataxia telangiectasia.