During pregnancy, what happens to hemoglobin concentration as blood volume increases?

• A. It typically declines due to hemodilution
• B. It increases due to erythropoiesis
• C. It remains unchanged
• D. It becomes macrocytic

Answer: (A)

During pregnancy, plasma volume expands substantially while red blood cell mass rises only modestly. This disproportionate increase dilutes the blood, so the hemoglobin concentration falls even though total red cell mass is up. This physiologic anemia of pregnancy happens because the body makes more plasma to support fetal growth and uterine expansion, but red cell production doesn’t keep pace with the larger plasma volume. Hemoglobin concentration isn’t typically higher or unchanged, and macrocytosis isn’t a characteristic feature of this state.