Risk factors

Many things can increase your risk of developing DVT. The more risk factors you have, the greater your risk of DVT. Risk factors for DVT include:

• Age. Being older than 60 increases your risk of DVT, though it can occur at any age.
• Sitting for long periods of time, such as when driving or flying. When your legs remain still for hours, your calf muscles don't contract. Muscle contractions normally help blood circulate.
• Prolonged bed rest, such as during a long hospital stay, or paralysis. Blood clots can form in the calves of your legs if your calf muscles don't move for long periods.
• Injury or surgery. Injury to your veins or surgery can increase the risk of blood clots.
• Pregnancy. Pregnancy increases the pressure in the veins in your pelvis and legs. Women with an inherited clotting disorder are especially at risk. The risk of blood clots from pregnancy can continue for up to six weeks after you have your baby.
• Birth control pills (oral contraceptives) or hormone replacement therapy. Both can increase your blood's ability to clot.
• Being overweight or obese. Being overweight increases the pressure in the veins in your pelvis and legs.
• Smoking. Smoking affects blood clotting and circulation, which can increase your risk of DVT.
• Cancer. Some forms of cancer increase substances in your blood that cause your blood to clot. Some forms of cancer treatment also increase the risk of blood clots.
• Heart failure. This increases your risk of DVT and pulmonary embolism. Because people with heart failure have limited heart and lung function, the symptoms caused by even a small pulmonary embolism are more noticeable.
• Inflammatory bowel disease. Bowel diseases, such as Crohn's disease or ulcerative colitis, increase the risk of DVT.
• A personal or family history of DVT or PE. If you or someone in your family has had one or both of these, you might be at greater risk of developing DVT.
• Genetics. Some people inherit genetic risk factors or disorders, such as factor V Leiden, that make their blood clot more easily. An inherited disorder on its own might not cause blood clots unless combined with one or more other risk factors.
• No known risk factor. Sometimes, a blood clot in a vein can occur with no apparent underlying risk factor. This is called an unprovoked VTE.