Preventing deep vein thrombosis (DVT) comes down to keeping blood moving, managing known risk factors, and using medical prevention when your risk is elevated. Most DVTs form when blood pools in the deep veins of your legs, slows down, and clots. The good news: many of the most effective prevention strategies are simple and within your control.
Why Blood Clots Form
Three conditions set the stage for a DVT: slow blood flow, damage to a vein wall, and blood that clots more easily than normal. Anything that triggers one or more of these raises your risk. Sitting or lying still for hours slows circulation in your legs. Surgery, fractures, and severe muscle injuries can damage veins directly. Pregnancy, estrogen-based birth control, and hormone replacement therapy all shift your blood chemistry toward easier clotting.
Certain chronic conditions also increase risk, including heart disease, lung disease, cancer, and inflammatory bowel disease. A personal or family history of blood clots, an inherited clotting disorder, older age, and obesity all add to the picture. The more of these factors you have at the same time, the higher your overall risk.
Stay Moving Throughout the Day
Regular movement is the single most accessible way to prevent DVTs. When your calf muscles contract, they squeeze the deep veins in your legs and push blood back toward your heart. Sitting or lying still for long stretches removes that pumping action and lets blood pool.
If you work at a desk, stand up and walk around periodically. While seated, you can keep circulation going with simple exercises: raise and lower your heels while keeping your toes on the floor, then reverse it by lifting your toes while your heels stay planted. Tightening and releasing your leg muscles also helps. These micro-movements won’t replace a walk, but they keep your calf pump active when you can’t get up.
Preventing Clots During Travel
Flights and long car rides are a well-known DVT trigger because you’re stuck in a cramped seat with your legs bent for hours. The CDC recommends getting up to walk every two to three hours on flights longer than four hours. Choose an aisle seat when you can so you don’t have to climb over anyone.
When you can’t leave your seat, do the same calf exercises described above: toe raises, heel raises, and leg muscle squeezes. Wearing moderate-pressure compression stockings (15 to 20 mmHg) during travel helps prevent blood from pooling in your lower legs. Stay hydrated too. Even mild dehydration can thicken your blood within about four hours, which is roughly the length of time you’d be sitting on a medium-haul flight. Drink water consistently rather than relying on alcohol or caffeine, both of which can dehydrate you further.
Compression Stockings: Choosing the Right Pressure
Compression stockings apply graduated pressure to your legs, tightest at the ankle and looser as they go up. This helps push blood upward and prevents pooling. They come in several pressure levels:
- Mild (8 to 15 mmHg): Light support for minor swelling and fatigue
- Moderate (15 to 20 mmHg): The standard range for DVT prevention during travel and for mild varicose veins
- Firm (20 to 30 mmHg): Typically used for moderate swelling, varicose veins, and post-surgical recovery
- Extra firm (30 to 40 mmHg): Reserved for severe venous disorders and advanced DVT cases
For general prevention, 15 to 20 mmHg stockings are the sweet spot. Higher pressures are usually prescribed by a doctor for specific conditions. Proper fit matters: stockings that are too tight can actually restrict circulation, and ones that are too loose won’t do much. Measure your calf and ankle circumference and check the sizing chart before buying.
After Surgery: What to Expect
Major surgery, especially involving the hip, knee, pelvis, or abdomen, is one of the highest-risk situations for DVT. Hospitals take this seriously. You’ll likely receive some combination of mechanical prevention (inflatable cuffs that squeeze your legs rhythmically, compression stockings, or foot pumps) and blood-thinning medication.
After major joint replacement, blood thinners are typically continued for at least 10 to 14 days, and often up to 35 days after hip replacement surgery. Your surgical team will start these medications either shortly before or within 12 hours after your procedure. If you’re at high risk for bleeding, mechanical compression alone may be used instead.
The most important thing you can do after surgery is follow instructions about getting up and moving as soon as your care team says it’s safe. Early walking, even just a few steps to the bathroom, is one of the most effective ways to restart circulation in your legs. Don’t skip your prescribed blood thinners because you feel fine. Clots often form silently in the days and weeks after surgery.
Hydration and Blood Thickness
Dehydration makes your blood thicker and stickier, which means it flows more slowly through your veins. Studies in aviation and environmental medicine show that even mild dehydration can measurably increase blood viscosity within four hours. This is especially relevant during air travel, hospital stays, and hot weather, all situations where people tend to drink less water than usual.
There’s no magic amount of water that prevents clots, but the principle is straightforward: if your urine is dark yellow, you’re not drinking enough. Consistent water intake throughout the day keeps blood flowing more freely.
Pregnancy and DVT Risk
Pregnancy increases DVT risk because of hormonal changes that make blood clot more easily, pressure from the growing uterus on pelvic veins, and reduced mobility in later months. That elevated risk continues for up to three months after delivery.
Not every pregnant person needs blood thinners. The American Society of Hematology recommends preventive anticoagulation during pregnancy primarily for those with a personal history of blood clots or certain inherited clotting disorders, such as being homozygous for factor V Leiden, having antithrombin deficiency, or having combined clotting conditions. For lower-risk inherited conditions like being heterozygous for factor V Leiden or having protein C or S deficiency alone, preventive medication is generally not suggested during pregnancy.
For all pregnant people, staying active, wearing compression stockings, and staying hydrated are the baseline prevention strategies. If you have a known clotting disorder or a history of DVT, bring it up early in your prenatal care so your provider can plan accordingly.
Know the Warning Signs
Prevention works best when paired with awareness. A DVT in your leg typically causes swelling, pain that feels like a deep cramp or charley horse, warmth, and sometimes a purplish discoloration of the skin. These symptoms usually affect one leg, not both.
The more dangerous scenario is when a clot breaks free and travels to the lungs, causing a pulmonary embolism. Signs of that include sudden unexplained shortness of breath, chest pain that worsens when you breathe deeply (sometimes described as a shooting pain from front to back), coughing up more than a trace of blood, a racing heart, and a drop in blood pressure that can leave you dizzy, sweaty, or confused. A pulmonary embolism is a medical emergency. If you notice these symptoms, especially after surgery, a long trip, or a period of immobility, get help immediately.
If you have varicose veins, watch for a vein that suddenly hardens, bulges when you lie flat, or becomes surrounded by tender, red skin. These changes can signal a clot forming near the surface that could extend into deeper veins.