Change in erythropoiesis with gestational age during pregnancy.

To investigate the changes in erythropoiesis during pregnancy, 342 pregnant and postpartum women were examined for reticulocyte subpopulations, reticulocyte maturity index (RMI), and serum transferrin receptor (sTfR) levels. The reticulocyte subpopulations were analyzed by flow cytometry, and the sTfR concentration was measured by an immunoenzymometric method. There were no significant differences in the values of reticulocyte subpopulations, RMI, and sTfR between first trimester and non-pregnant women. However, the RMI and sTfR concentration increased gradually from the second trimester of pregnancy, during which time values were twofold higher than those in the first trimester, and peaked in the third trimester. Then the RMI and sTfR values decreased abruptly 1-4 weeks postpartum and finally dropped to the levels of non-pregnant women 5 weeks after delivery. The maternal sTfR concentration correlated significantly with the corrected reticulocyte count (r = 0.52, P < 0.01), RMI (r = 0.67, P < 0.01), and high fluorescence reticulocytes (HFR) (r = 0.62, P < 0.01); however, the serum ferritin level correlated poorly with the reticulocyte subpopulations during pregnancy. In conclusion, erythropoiesis increases with gestational age during pregnancy and returns to normal 5 weeks after delivery. Measurement of sTfR in combination with RMI may improve the assessment of erythropoietic activity during pregnancy.