Heredity is a primary factor in over 80% of varicose vein cases. Other contributing factors may include pregnancy, obesity, hormone therapy, and standing or sitting for long periods of time. Varicose veins have been shown to be an inherited trait that can develop as early as 10 years old. If you have 1 parent with varicose veins you have a 40% chance of developing them yourself. If both parents have varicose veins that number jumps to 90%.