Causes and Risk Factors of Deep Vein Thrombosis

Deep vein thrombosis (DVT) is a condition that occurs when 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.

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Common Causes

Anything that interferes with your blood circulating like it should can cause DVT. Certain medical conditions, such as inflammatory bowel disease and some cancers, are associated with an increased risk for DVT.

Here are some other common causes to be aware of:

Immobility

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 who 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 lead to blood clots. Postpartum DVT can also be caused by damaged blood vessels in the uterus and pelvic area after giving birth.

Women are five times more likely to develop a blood clot when they are pregnant. A blood clot can happen any time throughout pregnancy and 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 form 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 the progestin hormones desogestrel and drospirenone are more likely to cause blood clots than other birth control pills. This includes Yaz, Yasmin, Beyaz, and Safyral. 

It's important to note that overall risk is relatively low. 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.

Risk of developing a clot increases about two-fold when taking the pill and about four-fold when on the patch, vaginal ring, or birth control pills containing desogestrel and drospirenone. For comparison, pregnancy presents the highest risk, which is about six times higher than not being on birth control.

If you have a family history of blood clots and want to take birth control pills, talk to your doctor about your risks. Other birth control options are available, such as progestin-only contraceptives or an intrauterine device (IUD).

Deep Vein Thrombosis Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Woman

Injury

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. 

Genetics

You also have an increased risk of developing DVT if you have a genetic blood clot disorder. Also known as inherited thrombophilias, genetic blood clot disorders are caused by specific gene mutations that increase the risk of developing abnormal blood clots. Thrombophilia can cause DVT on its own or compound the risk associated with the factors above.

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

Factor V Leiden thrombophilia and hereditary antithrombin deficiency (antithrombin III deficiency or AT III deficiency) are other examples of inherited thrombophilias.

You may have a genetic blood clot disorder 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 a genetic blood clot disorder, talk to your doctor about getting tested. 

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

Lifestyle Risk Factors

DVT can happen to anyone, but there are certain lifestyle habits that are associated with an increased risk for developing the condition.

The following are considered modifiable risk factors:

Inactivity

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 higher 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 impaired 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.

Smoking

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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