Real Dictionary

alpha-fetoprotein in American English
a protein in the blood of a normal fetus, occasionally reappearing in an adult, where its presence indicates the possibility of disease or, in a pregnant woman, of fetal malformations
noun: a serum protein produced during pregnancy, useful in the prenatal diagnosis of multiple births or birth defects

alpha-fetoprotein in British English
noun: a protein that forms in the liver of the human fetus. Excessive quantities in the amniotic fluid and maternal blood may indicate spina bifida in the fetus; low levels may point to Down's syndrome