Thrombosis can sometimes occur for no apparent reason at all. However, the risk of developing thrombosis is increased in certain circumstances or lifestyle.

Inactivity of the body tends the blood to collect in the lower parts of the body, usually in lower legs. There is nothing to worry about if this happens normally as when you start to move, the blood flow increases and circulates evenly in the body. However, if you are unable to move after a longer period of time, such as before and after an operation or during an illness or an injury or during a very long journey, the blood is forced to slow down considerably.

While in hospital, during the operational procedure, the risk of getting blood clot increases. The chances of developing thrombosis increases if an operation takes longer than 90 minutes and if it involves leg, hip and abdomen. If the operation is to treat inflammatory or abdominal condition such as appendicitis the chances of thrombosis may increase. When admitted to hospital, you will be assessed for your risk of developing a blood clot and would be given necessary preventive treatments for the same.

The wall of the blood vessel can become narrowed or blocked and can cause  blood clot to form if the blood vessel is damaged.

Pregnancy is also one of the causes of a certain type of thrombosis called Venous thromboembolism or VTE. Although chances of getting affected by the same is about one in 100,000 women of childbearing age. Other factors that can cause thrombosis during pregnancy include being over 35 years old and pregnant, expecting two or more babies, having a cesarean delivery, smoking and dehydration.

In case of women, combined contraceptive pill and hormone replacement therapy both contain female hormone estrogen. This increases the chances of internal clotting. Although there are no risks involved in taking progesterone-only contraceptive pills.