Iron deficiency anemia is common problem during pregnancy. Red cell size variation (anisocytosis) is the earliest morphologic changes in iron deficiency anemia. Red cell distribution width is a quantitative measure of red cell size variation and it can give the idea of early iron deficiency before other test to become positive.190 pregnant women were included in this study. Red cell distribution width was compared between iron deficient & non-iron deficient pregnant women. Red cell distribution width also compared with Hb level, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration and peripheral blood film in prelatent iron deficiency, latent iron deficiency, mild and moderate iron deficiency anemia.