Causes and Risk Factors of Deep Vein Thrombosis

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Deep vein thrombosis (DVT) happens when the blood flow slows down and its platelets and plasma don't properly mix and circulate. This causes a blood clot, in this case in a deep vein, which prevents deoxygenated blood from returning to the heart. Anyone can get DVT at any time, but there are risk factors that can increase your chances of developing this condition. For example, women who are pregnant or taking birth control are at risk of developing blood clots. If you live with a chronic condition like heart disease or cancer, you're also at risk of DVT.

deep vein thrombosis causes and risk factors

Common Causes

Anything that interferes with your blood circulating like it should can cause DVT. Here are some common causes to be aware of:


This is one of the biggest causes of DVT. When you're active, your leg muscles help keep your blood moving. However, when you are sedentary for too long, the opposite can happen, causing blood clots.

This is particularly why DVT is such a concern for people on bed rest (say, in a hospital setting), those have medical conditions that prevent them from walking, and those who drive long distances or travel on long flights and are stationary for longer than four hours.

Pregnancy and Postpartum

While DVT during pregnancy is rare, increased pressure in the veins in the pelvic area and legs can cause blood clots. Postpartum DVT can happen from damaged blood vessels in the uterus and pelvic area after giving birth.

According to the American Pregnancy Association, women are most likely to experience a blood clot in their first three months of pregnancy or in the first six weeks after giving birth. The American College of Obstetricians and Gynecologists also notes that the following pregnant women are more likely to develop DVT:

  • Those with a strong family history of DVT
  • Women with inherited thrombophilia (a genetic blood clot disorder, see below)
  • Those who need bed rest
  • Women who have a Cesarean birth

Birth Control Use

Research shows that women who take combination hormonal birth control (estrogen and progestin) have an increased chance of developing DVT. This includes birth control pills, the patch, and the vaginal ring, though the Pill presents a lower risk than the other two options.

But research shows that not all birth control pills are equal in terms of risk. Those containing progestin hormones desogestrel and drospirenone are more likely to cause blood clots than other birth control pills. This includes Yaz, Yasmin, Beyaz, and Safyral. 

For every 100,000 women ages 15 to 44 years who are not taking the Pill, approximately five to 10 are likely to develop a blood clot in a year. 

This risk increases three to four times in women using second-generation birth pills and six to eight times in those using third-generation ones, according to a study in the Journal of Pharmacology & Pharmacotherapeutics.

Still, even though DVT risk is higher in women who use combination birth control, the overall risk is still relatively low. If you have a family history of blood clots and want to take birth control pills, talk to your doctor about your risks. There are other birth control options out there, such as progestin-only contraceptives or an intrauterine device (IUD).

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When an injury occurs, either accidentally or intentionally as the result of a surgical incision, the proteins in your blood (clotting factors) coagulate at the site of the wound to form a blood clot. This prevents bleeding, but sometimes the blood clot can form inside one of the deep veins in the body and develop into DVT. 


You also have an increased risk of developing DVT if you have a genetic blood clot disorder, which can cause DVT on its own or compound risk associated with the above.

In fact, some studies have shown that 60 percent of DVT cases are due to genetic factors.

For example, people living with factor V Leiden thrombophilia have a specific gene mutation that increases their chances of developing blood clots.  

Prothrombin 20210 mutation, also known as factor II mutation, is another inherited blood clot disorder. Prothrombin is a protein in the blood that helps with coagulation. Someone with prothrombin 20210 mutation has too much if the protein in their blood, which makes them more likely to develop clots.

You may have prothrombin 20210 mutation if you or a family member has had a DVT or pulmonary embolism (PE), has suffered from a blood clot in an unusual site, has had a heart attack or stroke at a young age, or has a history of miscarriages. If you think you might have prothrombin 20210 mutation, talk to your doctor about getting tested. 

Hereditary antithrombin deficiency (antithrombin III deficiency or AT III deficiency) is a disorder that increases the risk of developing DVT and PE.

About 50 percent of people with hereditary antithrombin deficiency will develop one or more clots in their lifetime, according to the National Institutes of Health (NIH).

Pregnancy, use of birth control pills, surgery, age, and being inactive can all increase the risk. 

Lifestyle Risk Factors

DVT can happen to anyone, but your risk is greater if you're 60 years of age or older. Risk of DVT is also higher for people with certain diseases and conditions, such as inflammatory bowel disease and certain cancers.

While those are not things you can change, there are some risk factors that are modifiable.


This fits hand-in-hand with the risk posed by being immobile for long periods of time. A lack of regular exercise can impact your circulation and lead to DVT. 

Overweight and Obesity

Being overweight or obese can also put you at high risk of DVT for a few reasons. The added pressure the weight puts on your body can impact your veins and, therefore, blood flow.

In addition, when you are overweight or obese, your heart has to work harder to pump blood throughout your body. This added stress on the heart can lead to limited heart function and congestive heart failure, which significantly increases the chances of DVT and pulmonary embolism. 

If you undergo bariatric surgery for weight loss, know that DVT is one of the most common complications of the procedure.


Studies have shown that cigarette smoking is associated with an increased risk for DVT. While research doesn't prove that smoking directly causes DVT, people who smoke are at risk of being overweight or obese, having heart disease and stroke, and developing cancer—all of which are risk factors for DVT. 

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