What causes physiological anemia during pregnancy?

Physiological anemia during pregnancy occurs primarily due to an increase in plasma volume. During pregnancy, a woman's body experiences significant changes to support the growing fetus, including an expansion of the blood volume to ensure adequate blood flow to both mother and baby. This increase in plasma volume is proportionally greater than the increase in red blood cells, leading to a dilutional effect of hemoglobin and hematocrit levels.

As a result, while the number of red blood cells does increase during pregnancy, the greater increase in plasma volume ultimately leads to a lower concentration of red blood cells in the blood, which is why anemia can occur. This condition is termed "physiological anemia" since it is a normal adaptation to pregnancy rather than a pathological state.

Increased dietary iron needs and a decrease in red blood cell production could contribute to other types of anemia, but they do not primarily cause the physiological changes observed during pregnancy. The rise in cardiac output is related to the body's effort to accommodate increased uteroplacental blood flow but is not the direct cause of physiological anemia.