Deep Vein Thrombosis (DVT) occurs when blood clots form in the deep veins of your body, most often in your legs. DVT is dangerous because, if left untreated, the clots formed in the legs can break away and travel to the lungs, causing life-threatening conditions like pulmonary embolism. Untreated DVT may also result in lifelong swelling and deformity of the extremities. There are a number of reasons why your blood may clot, resulting in DVT. Here are a few of the most common causes of the condition:

Immobility and Trauma

When you don’t move for long periods of time, the blood in your veins will stay stagnant. This means that blood may pool in your extremities—especially your legs—and when blood pools, DVT may occur. This is why people who suffer from trauma such as broken legs or hips often develop DVT, because they are rendered immobile until their injury heals.

Pregnancy

Pregnant women are 10 times more likely to develop DVT than non-pregnant women of the same age, with the risk of DVT increasing as pregnancy progresses. This increased risk during pregnancy is a result of many factors. First, the weight a woman gains during pregnancy puts a lot of pressure on the veins in the pelvis and legs. This may damage those veins, making it harder for them to move blood through the area. Further, pregnancy actually changes the makeup of a woman’s blood and makes it more likely to clot. This is the body’s way of ensuring that the woman won’t lose too much blood during childbirth. Pregnancy hormones also make a pregnant woman’s blood flow much slower, another risk factor for DVT.

Obesity

Obesity can cause DVT for a number of reasons. People who are obese tend to lead less active lifestyles that result in decreased blood flow and a higher risk for DVT. Additionally, if you’re carrying extra fat around your belly, it puts extra stress on those veins and makes it more difficult for them to efficiently move blood through the area. Finally, obesity can actually change the makeup of your blood, increasing the occurrence of coagulation and, in turn, the risk of blood clot.

Other risk factors for DVT include:

Heredity—You are much more likely to develop DVT if you have a family history of the condition.
Age—People over the age of 60 are more likely to experience DVT. As we grow older, our veins become weaker and blood flow decreases.
Smoking—It alters the makeup of the blood and makes it more likely to clot and less able to flow freely.