Which statement best describes circulatory changes during pregnancy?

• A. Blood volume increases up to 50% to meet fetal needs.
• B. Blood volume decreases during pregnancy.
• C. Cardiac output decreases.
• D. RBCs decrease.

Answer: (A)

During pregnancy the circulatory system must support both the mother and the growing fetus, so several adaptations occur. The most important change is a substantial expansion of blood volume. Plasma volume climbs by about half, while red cell mass also increases but to a lesser extent, so the total blood volume rises roughly 40–50%. This extra volume helps perfuse the uterus and placenta and prepares the body for blood loss at delivery. Because plasma expands more than red cells, the blood becomes more dilute, leading to a lower hematocrit—this is normal and not a sign of disease.

Along with the rise in blood volume, cardiac output increases significantly (due to higher heart rate and greater stroke volume), and systemic vascular resistance falls to accommodate the increased flow. These coordinated changes support fetal needs and maternal circulation.

So the statement describing a large increase in blood volume to meet fetal needs best captures the circulatory changes during pregnancy. The other options describe decreases in blood volume, decreases in cardiac output, or decreases in RBCs, which do not align with the physiological adaptations that occur.