What physiological change contributes to hemodilution in pregnant patients?

In pregnant patients, the physiological change that significantly contributes to hemodilution is the increased plasma volume. During pregnancy, there is a marked rise in the overall blood volume, primarily due to an increase in plasma volume, which can expand by as much as 40-50%. This increase in plasma volume occurs to accommodate the growing fetus and support the increased metabolic demands of both the mother and the fetus.

As the plasma volume increases, it dilutes the concentration of red blood cells, leading to a lower hemoglobin level relative to the volume of blood. This state is often referred to as physiological hemodilution, which is typical in pregnancy. It is important to understand that while the absolute number of red blood cells may increase, the more significant rise in plasma volume results in a reduced hematocrit percentage.

In contrast, factors like reduced erythropoiesis and decreased red blood cell lifespan do not primarily drive this process in pregnancy. The body compensates for the increased demand for oxygen and other factors through enhanced erythropoietin production, stimulating the production of red blood cells. Additionally, blood viscosity tends to decrease due to the hemodilution effect rather than increase, making it easier for the heart to pump blood. Thus,