Preventing venous thromboembolism (VTE) depends on the situation: whether you’re heading into surgery, recovering in a hospital bed, taking a long flight, or managing ongoing risk factors like hormonal birth control or a clotting disorder. The core strategies fall into three categories: blood-thinning medications, compression devices, and movement. Which combination you need depends on your personal risk level.
How VTE Risk Is Assessed
Hospitals use scoring systems to decide who needs prevention and how aggressive it should be. The most widely used is the Caprini Risk Assessment Model, which assigns points based on factors like age, obesity, cancer, prior blood clots, type of surgery, and how long you’ll be immobilized. The 2013 version groups patients into four categories: low risk (0 to 1 points), moderate risk (2 points), high risk (3 to 4 points), and highest risk (5 or more points). Each category triggers a different level of prevention.
Someone young and healthy having a minor procedure might score a 0 and need nothing beyond getting up and walking soon after. Someone over 60 having major abdominal surgery with a history of clots could score well above 5, putting them in the highest-risk group where both medication and compression devices are recommended simultaneously. Every hospital is expected to have a formal strategy for assessing and preventing VTE in all admitted patients.
Blood-Thinning Medications
For moderate to high-risk patients, the primary prevention tool is a prophylactic dose of an anticoagulant, a much lower dose than what’s used to treat an existing clot. These medications slow your blood’s ability to form clots in the deep veins, particularly in the legs and pelvis where blood flow can stagnate during bed rest.
The choice of medication depends on the clinical scenario. For major general, gynecologic, or urologic surgery, low-dose injectable anticoagulants are the standard. For hip and knee replacement, oral options are also available and are often preferred because they don’t require injections. The duration matters as much as the medication itself: after hip or knee replacement or hip fracture surgery, prophylaxis should continue for a minimum of 10 days and ideally up to 35 days, since clot risk persists well after you leave the hospital.
Aspirin alone is not considered adequate prevention for any patient group. While it affects platelets, it doesn’t target the clotting cascade in the way that’s needed to prevent deep vein clots.
Compression Devices and Stockings
Mechanical prevention works by physically squeezing the legs to keep blood moving through the veins. There are two main forms: graduated compression stockings, which apply steady pressure (typically 15 to 30 mmHg at the ankle), and intermittent pneumatic compression devices, which are inflatable sleeves that rhythmically squeeze and release around the calves or legs.
A meta-analysis of 11 trials found that stockings providing 15 to 20 mmHg of pressure reduced swelling and symptoms compared to stockings below 10 mmHg or no compression at all. Interestingly, there was no significant additional benefit from going above 20 mmHg compared to the 10 to 20 mmHg range, meaning moderate-pressure stockings are effective without being uncomfortably tight.
Mechanical methods are used in two main situations: as the sole prevention for patients who are at high risk of bleeding and can’t safely take blood thinners, or as an add-on to medication for patients in the highest risk category. They shouldn’t be used on legs with open fractures that haven’t been stabilized, large open wounds, or external fixators and splints in place.
Getting Moving Early After Surgery
Walking soon after surgery is one of the most effective things you can do to lower your clot risk. The data on this is striking. In one study of patients after knee replacement, those who were mobilized within 24 hours had a VTE rate of 1%, compared to 28% in the control group. Another study in patients after gastric bypass surgery found a VTE rate of 0.5% with early ambulation (within 2 hours) versus 2.7% with standard care. A third study showed rates of 16% versus 38% in knee replacement patients who were mobilized within the first day compared to those who waited longer.
The pattern is consistent across surgical types: the sooner and more frequently you walk, the lower your risk. Even short sessions of 15 to 30 minutes, done at least twice daily, make a measurable difference. If you can’t walk, flexing your ankles repeatedly (pumping your calf muscles) helps push blood back toward the heart and reduces stagnation in the deep leg veins.
Prevention During Long Travel
Flights and other travel lasting more than four hours increase VTE risk, though the risk for flights under four hours is negligible. The concern is prolonged sitting in a cramped position, which allows blood to pool in the lower legs.
For travelers on journeys exceeding six hours, the American College of Chest Physicians recommends frequent walks through the cabin, calf muscle exercises while seated, choosing an aisle seat for easier movement, and wearing properly fitted below-the-knee compression stockings that provide 15 to 30 mmHg of pressure at the ankle. These same principles apply to long car or train rides. Staying hydrated helps too: dehydration concentrates the blood, increasing viscosity and making clots more likely to form.
Hormonal Birth Control and Clot Risk
Combined oral contraceptives (those containing both estrogen and progestin) significantly increase VTE risk, particularly in the first two years of use. A large UK Biobank study of 240,000 women found that VTE risk roughly tripled during the first two years on the pill (hazard ratio of 3.09), but this elevated risk disappeared with continued use beyond that window.
This doesn’t mean everyone on the pill will develop a clot. The baseline risk of VTE in young women is very low, so even tripling it still leaves the absolute risk small. But the risk compounds when combined with other factors like obesity, smoking, inherited clotting disorders, or prolonged immobility. If you have a family history of blood clots or a known thrombophilia, this is worth discussing with your prescriber, as progestin-only methods or non-hormonal options don’t carry the same risk.
After Pregnancy and Cesarean Delivery
Pregnancy itself increases clot risk because of hormonal changes and pressure on pelvic veins, and that risk peaks in the weeks after delivery. Women who undergo cesarean delivery and have a personal history of blood clots or an inherited clotting disorder are recommended to receive both compression devices (starting before surgery and continuing until they’re walking) and blood-thinning medication for six weeks after delivery.
Even without a prior clot history, women with multiple risk factors after cesarean delivery may benefit from combined prevention. The American College of Obstetricians and Gynecologists recommends that when risk factors persist into the postpartum period, pharmacologic prevention for up to six weeks should be considered. The key risk factors include obesity, cesarean delivery (especially emergency), preeclampsia, prolonged bed rest, and older maternal age.
Prevention in Hospitalized Medical Patients
VTE prevention isn’t just for surgical patients. People admitted to the hospital with acute medical illnesses, including heart failure, severe respiratory disease, infections, and inflammatory conditions, also face elevated clot risk from a combination of inflammation and immobility. Guidelines recommend that these patients receive prophylactic anticoagulation during their hospital stay.
Critically ill patients in intensive care units should be assessed for VTE risk on admission, and most will receive some form of prevention. For those at high bleeding risk, intermittent pneumatic compression devices alone are a reasonable alternative. The goal is the same across all hospital settings: keep blood moving and reduce clotting tendency during the period of highest vulnerability.