What changes occur in a pregnant woman's blood volume?

During pregnancy, a woman's blood volume increases significantly, typically by about 30-50%. This increase is crucial for several reasons. As the fetus grows, the mother’s body needs to supply adequate oxygen and nutrients, which necessitates a higher volume of blood circulation. The increased blood volume also helps accommodate the demands of the placenta and supports increased metabolic needs during pregnancy.

This expansion of blood volume is a physiological adaptation that helps prevent complications such as hypotension, maintains uteroplacental perfusion, and provides sufficient reserve blood volume for the mother and fetus during delivery. Ideally, this significant increase helps offset the blood loss that may occur during childbirth, ensuring that the mother can sustain both her health and that of her newborn.

Other options reflect misunderstandings about how the body adapts to pregnancy. A decrease in blood volume would not support the increased demands of a developing fetus and could lead to serious complications. A constant blood volume does not account for the physiological changes and demands of pregnancy, while a limited increase only during the first trimester would not meet the ongoing needs of both the mother and growing fetus throughout the entire pregnancy.