Physiologic anemia of pregnancy occurs because of which change in blood volume?

• A. An increase in red blood cell mass exceeds plasma volume
• B. A decrease in plasma volume
• C. A decrease in blood volume
• D. An increase in plasma volume in excess of increase in red blood cells

Answer: (D)

Physiologic anemia of pregnancy comes from dilution of the blood because plasma volume expands far more than the red blood cell mass. As pregnancy progresses, the body increases circulating plasma to support the growing uterus and placenta, but the red cell mass rises only modestly in comparison. The result is more plasma relative to red cells, lowering hemoglobin concentration and hematocrit—this dilutional effect is normal and expected during pregnancy.

If red cell mass increased more than plasma, hematocrit would rise, not fall, so that option wouldn’t explain the anemia. A decrease in plasma or overall blood volume would concentrate the blood rather than dilute it, also not matching physiologic pregnancy changes. The key idea is the plasma volume increases in excess of red blood cell production, producing the mild dilutional anemia seen in most pregnant individuals.