Erythropoiesis in pregnancy.

The reticulocyte count, serum ferritin and serum erythropoietin concentrations were measured during the course of pregnancy in 41 women. A decrease in iron stores early in pregnancy was accompanied by a significant rise in the reticulocyte count until the 28th week. Erythropoietin levels did not rise significantly until the 28th week of pregnancy and had fallen to the post-natal level by 40 weeks. The results are consistent with an increase in erythropoietic activity early in pregnancy which did not appear to depend upon increased plasma erythropoietin levels.