Blood travels through veins to get from your cells back to your heart.  When blood is in the veins of your legs, the contraction of your leg muscles helps the blood flow against gravity to the heart.  During pregnancy, the volume of blood in your body increases to support the baby, but blood flow between the legs and pelvis decreases.  This causes pressure to build up in the veins, forcing them to expand outward.  The result is large, often visible, varicose veins.  Watch this video for the full scoop on pregnancy and varicose veins!