or  a-fetoprotein  or chiefly Brit  alpha-foetoprotein  or  a-foetoprotein  n :  a fetal blood protein present abnormally in adults with some forms of cancer (as of the liver) and normally in the amniotic fluid of pregnant women but with very low levels tending to be associated with Down's syndrome in the fetus and very high levels with neural tube defects (as spina bifida) in which the tube remains open .
 
 
 
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