What physiological change during pregnancy often leads to dilutional anemia?

During pregnancy, there is a significant increase in plasma volume, which can lead to dilutional anemia. As blood volume expands to support the growing fetus and to prepare for delivery, the increase in plasma volume exceeds the increase in red blood cell mass. While the body does produce more red blood cells, the relative increase in plasma volume creates a situation where the concentration of red blood cells within that increased blood volume becomes lower, which is referred to as dilutional anemia.

This physiological adaptation is crucial for maintaining adequate blood flow and nutrient delivery to both the mother and the fetus. The increase in plasma volume begins early in pregnancy and is one of the most pronounced changes, often reaching levels that can be 40-50% higher than normal by the third trimester.

In contrast, while erythropoietin synthesis does increase in response to the physiological demands of pregnancy, and iron absorption is also generally enhanced to meet the increased needs, the key factor leading to dilutional anemia is the marked increase in plasma volume. This highlights the body's adjustments to meet the increased physiological demands placed on it during pregnancy.