While heredity is the number one cause of vein disease, women are at higher risk than men, primarily because pregnancy runs a close #2, and significantly increases the likelihood of developing varicose veins.
Veins are the blood vessels that return blood from the extremities to the heart, so the blood in leg veins is already working against gravity. During pregnancy, additional factors take effect. The growing uterus puts pressure on the central vein on the right side of the body (the inferior vena cava), which in turn increases pressure in the leg veins. During pregnancy the amount or volume of blood in the body increases, further adding to the burden on the veins. In addition, hormone levels vary tremendously, such as rising progesterone levels which cause the vein walls to relax.
