During pregnancy, blood volume increases greatly. This can cause veins to enlarge. Plus, pressure on the large veins behind the uterus causes the blood to slow in its return to the heart. For these reasons, varicose veins in the legs and anus (hemorrhoids) are more common in pregnancy. 
Varicose veins look like swollen veins raised above the surface of the skin. They can be twisted or bulging and are dark purple or blue in color. They are found most often on the backs of the calves or on the inside of the leg. 
What might help: 
•    Avoid tight knee-highs. 
•    Sit with your legs and feet raised.