Objective: Based on previous studies that demonstrated lighter and larger erythrocytes in late pregnancy, we hypothesized that the life span of erythrocytes in late pregnancy is shorter than in nonpregnant women.
Methods: We used the density distribution of cells to evaluate the age distribution of erythrocytes in pregnant versus nonpregnant women and rats. The life span of erythrocytes was compared between pregnant rats and nonpregnant syngeneic rats of the same age using 51Cr for labeling erythrocytes.
Results: Based on the density distribution of cells, a similar shift to lighter erythrocytes was found comparing pregnant to nonpregnant women and rats. The pregnant rat erythrocytes had a shorter life span by 9.2% (33.6 versus 36.9 days; P = .0010).
Conclusions: The life span of erythrocytes in pregnant rats is shorter than in nonpregnant ones. A similar shift in the age distribution of pregnant rat and pregnant human erythrocytes is probably associated with a similar life span of pregnant rat and pregnant human erythrocytes. The shorter life span of erythrocytes in late pregnancy may be attributed to higher erythropoietin levels in pregnancy, which induce "emergency hematopoiesis" resulting in younger reticulocytes and macrocytic erythrocytes, which are known to have a shorter life span.