Intrinsic factor in human amniotic fluid as determined by radioimmunoassay

The intrinsic factor (IF) concentration in 55 human amniotic fluid specimens was determined by radioimmunoassay (RIA). The antiserum was produced by immunizing rabbits with the cobalamin-IF complex isolated from human gastric juice. The median concentration of IF was 0.17 nmol/l and the extreme values less than 0.07-2.51 nmol/l. Three specimens with a clearly elevated level (0.96, 1.11 and 2.51 nmol/l) were observed. The highest value was associated with a fetal malformation, viz. obstruction of the proximal gut. There was no evident correlation between the concentration of IF in amniotic fluid and gestational age.