How does pregnancy generally affect a woman's blood volume?

During pregnancy, a woman's blood volume generally increases. This physiological change is crucial to support both the mother and the developing fetus. The increase in blood volume helps accommodate the additional metabolic demands placed on the mother's body and ensures adequate nutrient and oxygen delivery to the fetus.

The increase typically starts in the first trimester and continues throughout pregnancy, peaking around the third trimester. This expansion of blood volume is primarily due to an increase in plasma volume, which helps to prepare the body for labor and delivery, as well as to prevent complications such as low blood pressure or inadequate blood flow to vital organs.

This significant increase in blood volume also leads to an increase in cardiac output, which is essential for maintaining proper circulation during the various changes that occur throughout pregnancy.