Red cell distribution width (RDW) changes in pregnancy.

OBJECTIVE: As part of an exercise in establishing normograms of hematological parameters in pregnancy, we studied the red cell distribution width (RDW) in healthy pregnant women. METHODS: A longitudinal study of RDW measurements in 121 pregnant women at 16 and 34 weeks gestation and during labor and at Days 3 and 7 postpartum. All the women had uncomplicated pregnancies, minimum hemoglobin (Hb) of 11.0 g/dl at recruitment and took iron supplements from 16 weeks of gestation and until 7 days after delivery. All subjects went into spontaneous labor, 110 achieving a normal vaginal delivery while the remaining 11 were delivered by cesarean section. Two-way analysis of variance was used to study the changes in RDW between any given gestations to test the variability between and within subjects. RESULTS: RDW increased significantly (P < 0.0001) between 34 weeks of gestation and the onset of labor. No significant changes occurred between 16 and 34 weeks gestation, or during the 7 days postpartum. CONCLUSION: This is the first longitudinal study analyzing the between and within women changes in RDW with progression of pregnancy. The unexpected rise in the RDW during the last 4-6 weeks leading up to the onset of labor suggests increased bone marrow activity. The stimulus is unknown, but as RDW changes are highly significant there may well be a useful indicator of impending parturition.