How pregnancy affects blood volume?

During pregnancy, a woman’s blood volume increases dramatically by about 40–50% compared to pre-pregnancy levels. This change starts early in the first trimester and peaks around the 32nd week. The reason is simple: the growing fetus and placenta need a reliable oxygen and nutrient supply, and the mother’s body must prepare for possible blood loss during delivery.

This increase mainly comes from an expansion in plasma volume (the liquid part of blood), which grows faster than red blood cell mass. As a result, blood becomes slightly diluted, leading to “physiologic anemia of pregnancy,” a normal and temporary condition.

Increased blood volume also helps the mother’s heart work more efficiently. Cardiac output rises by 30–50%, ensuring enough blood reaches both maternal organs and the uterus. The extra blood flow supports the kidneys, which must filter more waste from both mother and baby.

After delivery, blood volume gradually returns to normal within a few weeks. Proper hydration, iron intake, and rest help this transition. Overall, the rise in blood volume is a crucial adaptation that keeps pregnancy healthy and supports the baby’s growth and development.