Deep vein thrombosis (DVT) is a blood clot that develops within a deep vein in the body, usually in the leg.

Blood clots that develop in a vein are also known as venous thrombosis.

DVT usually occurs in a deep leg vein, a larger vein that runs through the muscles of the calf and the thigh.

It can cause pain and swelling in the leg and may lead to complications such as pulmonary embolism. This is a serious condition that occurs when a piece of blood clot breaks off into the bloodstream and blocks one of the blood vessels in the lungs.

Anyone can develop DVT, but it becomes more common over the age of 40. As well as age, there are also a number of other risk factors, including:

• Having a history of DVT or pulmonary embolism
• Having a family history of blood clots
• Being inactive for long periods – such as after an operation or during a long journey
• Blood vessel damage – a damaged blood vessel wall can result in the formation of a blood clot
• Having certain conditions or treatments that cause your blood to clot more easily than normal – such as cancer (including chemotherapy and radiotherapy treatment), heart and lung disease, thrombophilia and Hughes syndrome
• Being pregnant – your blood also clots more easily during pregnancy
• Being overweight or obese