Alpha-fetoprotein (AFP) is the main protein of fetal serum. It is
usually undetectable after birth. Alpha-fetoprotein is produced by the liver and the yolk sac of the
fetus, crosses the placenta, enters the amniotic fluid and can also be detected into the
maternal blood. It's the main protein during the first three months of development. AFP
greatly decreases by age 1 and should only be found in very
low levels in non-pregnant adults.
