Elevated serum erythropoietin concentration is associated with coordinated changes in red blood cell and reticulocyte indices of pregnant women at term.

The aim of this study was to evaluate the relationship between the erythropoietin (EPO) concentration and both the advanced cellular indices reflecting the haemoglobin contents of red blood cells and reticulocytes and the serum markers of iron status. The study population comprised pregnant women at term (n = 210). The serum EPO, transferrin receptor (TfR), ferritin, the percentages of hypochromic red blood cells (%HYPOm) or reticulocytes (%HYPOr) and the cellular haemoglobin in mature red blood cells (CHm) or in reticulocytes (CHr) were measured in maternal blood before delivery. The EPO concentration was elevated above the reference limit (>31.5 mIU/mL) in 16 % of all pregnant women, and appeared to correlate in a linear fashion, especially with %HYPOm (r = 0.52, p<0.001), %HYPOr (r = 0.57, p<0.001) and CHr (r = -0.45, p<0.001). The significant (p<0.05) predictors of EPO in the multivariate stepwise regression analysis were %HYPOr, Hb, %HYPOm and MCV. In general, the lower the cellular haemoglobin content, the higher the overall maternal EPO production. In conclusion, elevated %HYPOm and %HYPOr reflecting iron-deficient erythropoiesis are associated with an increase in EPO concentration in maternal blood. This could be explained by subclinical iron deficiency being accompanied by a compensatory EPO response.