Pregnancy increases your risk of blood clots by about four to five times compared to when you’re not pregnant, with roughly 1.72 cases of venous thromboembolism per 1,000 deliveries. The good news is that most pregnancy-related clots are preventable through a combination of movement, awareness, and sometimes medical intervention. Understanding why your body becomes more clot-prone during this time helps you take the right steps to protect yourself.
Why Pregnancy Makes Clots More Likely
Your body starts preparing for delivery long before labor begins, and part of that preparation involves ramping up your clotting ability. This makes biological sense: your body is getting ready to prevent excessive bleeding during birth. But it also tips the balance toward clot formation throughout pregnancy and the weeks that follow.
Several specific changes drive this shift. Your blood levels of key clotting proteins (factors VII, VIII, X, and fibrinogen) rise significantly, while protein S, one of your natural anticoagulants, drops. Your body also produces up to five times more of a substance that blocks clot breakdown, making any clots that do form harder to dissolve. On top of these blood chemistry changes, your growing uterus physically compresses the veins in your pelvis and legs, slowing blood flow. Hormonal shifts further relax and widen your veins, which means blood pools more easily. Add in the reduced mobility that often comes with later pregnancy, and you have a perfect setup for clot formation.
These changes begin in the first trimester and intensify as pregnancy progresses. The risk peaks just after delivery and remains elevated for up to six weeks postpartum.
Stay Active Throughout Pregnancy
Regular movement is your most powerful everyday tool against blood clots. When your calf muscles contract, they squeeze blood upward through your veins and back toward your heart, counteracting the pooling effect that pregnancy creates. Walking for 20 to 30 minutes most days keeps this pump working effectively.
If you’re on bed rest or having a day where fatigue keeps you off your feet, simple exercises still help. Flexing and pointing your feet, rotating your ankles in circles, and bending your knees repeatedly all activate the muscles that push blood through your leg veins. Doing these for a few minutes every hour makes a measurable difference in blood flow. Avoid sitting or lying in one position for long stretches. Even shifting your weight or elevating your legs periodically reduces stagnation in the veins.
Preventing Clots During Travel
Long-distance travel poses extra risk because you’re seated and relatively still for hours. The American College of Obstetricians and Gynecologists recommends moving your feet, toes, and legs frequently during any long trip, and getting up to walk around several times during a flight. On road trips, stop every one to two hours to stretch and walk.
Graduated compression stockings, which apply gentle pressure that’s strongest at the ankle and decreases up the leg, can help prevent blood from pooling during travel. These are available in below-the-knee and full-length versions. However, they need to fit properly. Stockings that are too tight or worn incorrectly can actually increase your clot risk. If you have diabetes or circulation problems, compression stockings may not be appropriate for you, so check with your provider before buying a pair.
Staying hydrated during travel also matters. Dehydration thickens your blood slightly, which compounds the other risk factors already at play. Keep water within reach and drink consistently rather than waiting until you feel thirsty.
Compression Stockings for Daily Use
Compression stockings aren’t just for travel. If you have additional risk factors for clots, such as a personal or family history of blood clots, obesity, or carrying multiples, wearing graduated compression stockings daily during pregnancy can reduce your risk. They work by gently pushing blood back up toward your heart and preventing it from collecting in your lower legs. Many women also find they reduce leg swelling and general discomfort, which is a practical bonus in the second and third trimesters.
When Medication Is Recommended
Some women have risk factors significant enough that lifestyle measures alone aren’t sufficient. If you’ve had a previous blood clot, have an inherited clotting disorder, or have multiple risk factors stacking up, your provider may recommend a blood-thinning medication called heparin. This is given as an injection under the skin rather than as a pill, because the oral blood thinners commonly used outside of pregnancy can harm the developing baby. Heparin does not cross the placenta and is considered safe for the fetus.
The duration varies depending on your risk level. Some women need heparin only for specific high-risk periods, like after a long flight. Others take it throughout pregnancy and for up to six weeks after delivery. If you were on heparin before giving birth, you’ll typically continue for at least six weeks postpartum, since the risk remains elevated during that window. Your provider will adjust the plan based on your individual situation and how your pregnancy progresses.
The Postpartum Period Matters Too
Many women focus on clot prevention during pregnancy and relax their guard after delivery, but this is actually when the risk is highest. The combination of tissue damage from birth, sudden hormonal shifts, and reduced mobility during recovery creates a vulnerable window. Whether you deliver vaginally or by cesarean section, the first days and weeks after birth deserve just as much attention as the months before.
Getting up and moving as soon as you safely can after delivery is one of the most effective things you can do. For vaginal births, this usually means walking within hours. After a cesarean, your care team will encourage you to stand and take short walks within a day, even though it’s uncomfortable. Continuing with ankle and foot exercises while in bed, staying hydrated, and wearing compression stockings if recommended all contribute to prevention during this critical period. If your provider prescribed heparin for 7 to 10 days or up to 6 weeks postpartum, staying consistent with those injections is important even when you’re exhausted and adjusting to life with a newborn.
Warning Signs to Recognize
Even with prevention, it’s important to know what a blood clot looks and feels like so you can act quickly. A clot in the leg or arm, known as a deep vein thrombosis, typically causes swelling in one limb (not both), pain or tenderness that isn’t from an injury, and skin that feels warm to the touch or looks red or discolored. During pregnancy, these symptoms are easy to dismiss as normal swelling or soreness, but the key difference is that a clot usually affects one leg noticeably more than the other.
The more dangerous scenario is when a clot breaks free and travels to the lungs, called a pulmonary embolism. Symptoms include sudden difficulty breathing, chest pain that gets worse when you take a deep breath or cough, coughing up blood, and a heart rate that feels unusually fast or irregular. A pulmonary embolism is a medical emergency. If you experience any combination of these symptoms during pregnancy or in the weeks after delivery, get emergency care immediately.