APA Dictionary of Psychology

n. a protein found in the blood plasma of fetuses and produced by some tumors in adult humans. In human fetuses, unusually high or low levels of this protein suggest fetal abnormality, as analysed through a prenatal alpha-fetoprotein test of blood samples drawn from pregnant women. In adult humans, measurement of alpha-fetoprotein is used to diagnose liver cancer. In rodents, alpha-fetoprotein binds estrogens and prevents them from entering the brain, thus influencing sexual differentiation.