Does the Volume of Blood Change during Pregnancy?

During pregnancy, a woman’s volume of blood generally increases by about 50% from her pre-pregnancy levels, with the majority of the increase taking place during the second trimester. This blood increase is to help the body adjust to an increased need for blood for the uterus and the metabolic needs of the fetus. There also is an increased amount of blood pumped to the organs, especially the kidneys. Varicose veins — dark-colored, swollen veins that develop on the legs — are common during late pregnancy and are caused by the extra blood volume.

More about blood volume during pregnancy:

• Blood volume tends to increase just slightly more for women who are carrying multiple fetuses, with approximately a 5% higher increase than in women who are carrying single fetuses.
• The risk of congestive heart failure can be higher during pregnancy because the heart has to work harder to pump the additional blood throughout the body.
• Increased blood volume can make delicate tissues, such as the gums and small blood vessels in the nose, more prone to damage and more likely to bleed because of a small amount of pressure.