Many factors increase a person's chances of developing varicose or spider veins. These include: Increasing age. As you get older, the valves in your veins may weaken and not work as well. Medical history. Being born with weak vein valves increases your risk. Having family members with vein problems also increases your risk. About half of all people who have varicose veins have a family member who has them too. Hormonal changes. These occur during puberty, pregnancy, and menopause. Taking birth control pills and other medicines containing estrogen and progesterone also may contribute to the forming of varicose or spider veins. Pregnancy. During pregnancy, there is a large increase in the amount of blood in the body. This can cause veins to enlarge. The growing uterus also puts pressure on the veins. Varicose veins usually improve within three months after delivery. More varicose veins and spider veins usually appear with each additional pregnancy. Body Mass Index. Being overweight or obese can put extra pressure on your veins. This can lead to varicose veins. Lack of movement. Sitting or standing for a long time may force your veins to work harder to pump blood to your heart.