What happens to red blood cell volume during pregnancy?

What happens to red blood cell volume during pregnancy?

• A. Increases 5-10%
• B. Increases 20-30% with hemodilution
• C. Decreases
• D. No change

Answer: (B)

During pregnancy, the body expands blood volume to support the fetus and prepare for delivery. Plasma volume increases more than red blood cell mass, so red cell volume does rise, but they are outpaced by the plasma. The red cell volume grows about 20–30% by the third trimester, while plasma volume expands even more, producing hemodilution. This combination yields a lower hematocrit—the physiologic anemia of pregnancy—yet RBC mass is still increased to help meet oxygen needs. So the increase in red cell volume with concurrent hemodilution explains why hematocrit drops even though red cells are actually more numerous. The other options don’t fit because RBC volume does increase (not decrease or stay the same), and the increase is larger than a 5–10% change.

During pregnancy, the body expands blood volume to support the fetus and prepare for delivery. Plasma volume increases more than red blood cell mass, so red cell volume does rise, but they are outpaced by the plasma. The red cell volume grows about 20–30% by the third trimester, while plasma volume expands even more, producing hemodilution. This combination yields a lower hematocrit—the physiologic anemia of pregnancy—yet RBC mass is still increased to help meet oxygen needs. So the increase in red cell volume with concurrent hemodilution explains why hematocrit drops even though red cells are actually more numerous. The other options don’t fit because RBC volume does increase (not decrease or stay the same), and the increase is larger than a 5–10% change.