Iron and erythropoiesis in normal subjects and in pregnancy.

Erythropoiesis is a highly dynamic process which may be monitored by quantitative reticulocyte counting. In chronic renal failure erythropoietin therapy can restore erythropoiesis to normal level. Occult infection and malignancy can limit this response and quantitative reticulocate counting can be used to identify this at an early stage. Iron supply may also be limiting and the measurement of percentage hypochromia is an effective means of detecting this. In pregnancy erythropoiesis is stimulated at a very early stage, direct measurement of red cell mass using a non-radioactive method has shown that half of the increase may occur within the first trimester. Recent studies suggest that erythropoiesis is stimulated very soon after conception.