Pregnant women are at an increased risk for varicose veins, which become swollen from the pooling of excess blood. There are several factors at work that may explain a relationship between pregnancy and varicose veins. For one, a woman's blood volume increases during pregnancy, putting additional strain on blood vessels. In addition, greater amounts of the hormone estrogen are produced, and estrogen is believed to relax the blood vessels. It's also been suggested that the expanding uterus may contribute to varicose veins because it puts additional pressure on veins in the pelvis, leading to the progressive rupture of valves further down. Pregnancy may also result in temporary changes in the calf muscles that help pump blood back to the heart. Still, doctors aren't sure if pregnancy actually causes varicose veins or simply makes them worse in women who are susceptible. In either case, most women's veins will improve within three months after delivery. For this reason, doctors advise delaying any treatment and re-evaluating the situation after the baby is born. Wearing compression stockings during pregnancy won't prevent varicose veins from appearing, but will often reduce symptoms like pain and cramping, and may have a protective effect on the deeper veins.