assuming that urination is the principle route by which alpha-fetoprotein ( a.f.p . ) passes into the amniotic fluid from the normal fetus , and that a.f.p . is mainly degraded by a process of fetal swallowing and digestion , 4 possible mechanisms by which amniotic-fluid a.f.p . is increased by fetal abnormalities are postulated . ( 1 ) amniotic-fluid a.f.p . is increased in open neural-tube defects by leakage of a.f.p . from fetal serum and cerebrospinal fluid . ( 2 ) in exomphalos exposure of blood-vessels in the extruding viscera permits transudation of a.f.p . into the amniotic fluid . ( 3 ) in nephrosis , fetal proteinuria increases amniotic-fluid a.f.p . ( 4 ) impaired fetal swallowing or digestion would account for increased amniotic-fluid a.f.p . in congenital malformations of the orogastrointestinal tract .
C0002210
alpha-fetoprotein
C0015965
fetal