The phrase "blood volume" refers to the amount of blood that is present in a person's body. It is a measure of how much blood is circulating within the blood vessels. Full definition
They are crucial to maintain increased blood volume, the growth and cellular development of your baby and a healthy placenta. (ohbabynutrition.com)
This leads to an increase in blood volume in these blood vessels. (mypetneedsthat.com)
But here's a pretty good reason for having salt when pregnant... it turns out that in pregnancy, there is an increase of blood volume in the body. (babygaga.com)