Pregnancy-Related Thrombosis
Blood clots that can form during pregnancy and after delivery
Quick Facts
- Type: Pregnancy-related vascular condition
- Higher-risk time: Pregnancy and the weeks after delivery
- Common sites: Leg veins (DVT), lungs (pulmonary embolism)
- Seek urgent care: Sudden breathlessness, chest pain, leg swelling
Overview
Pregnancy naturally increases the blood's tendency to clot. This is part of the body's preparation to limit bleeding during childbirth, but it also raises the risk of unwanted blood clots forming in the veins. These clots are known as venous thromboembolism, which includes deep vein thrombosis (a clot in a deep vein, usually in the leg) and pulmonary embolism (a clot that travels to the lungs).
The increased risk is present throughout pregnancy and is highest in the weeks immediately after delivery. Although clots are uncommon overall, they are a leading cause of serious illness around pregnancy, so recognizing the warning signs and managing risk factors is important. With awareness and, when needed, preventive treatment, the risk can be greatly reduced.
Symptoms
Symptoms depend on where the clot forms. A clot in a leg vein typically causes:
- Swelling of one leg, often the left
- Pain, tenderness, or cramping in the calf or thigh
- Warmth and redness or discoloration of the skin
A clot that travels to the lungs (pulmonary embolism) is an emergency and may cause:
- Sudden shortness of breath
- Chest pain that may worsen with breathing
- A fast heartbeat
- Coughing, sometimes with blood
- Lightheadedness or fainting
Because mild leg swelling is common in normal pregnancy, new swelling in only one leg deserves prompt attention.
Causes
Three factors that promote clotting are all increased in pregnancy:
- Increased clotting tendency: Hormonal changes raise the levels of clotting proteins in the blood.
- Slower blood flow: The growing uterus presses on large veins in the pelvis, and blood moves more slowly through the legs.
- Vein and vessel changes: Delivery, particularly cesarean section, and reduced movement can add to the risk.
These changes combine so that the clotting risk is several times higher during pregnancy and the weeks after birth than at other times of life.
Risk Factors
- A previous blood clot or a known inherited clotting disorder (thrombophilia)
- Cesarean delivery, especially as an emergency
- Prolonged bed rest or reduced mobility
- Obesity
- Older age and multiple previous pregnancies
- Carrying twins or more, and certain pregnancy complications
- Long-distance travel during pregnancy
Diagnosis
Doctors evaluate suspected clots carefully in pregnancy, choosing tests that are safe for the pregnancy.
- Leg ultrasound: The main test for a suspected deep vein thrombosis; it uses no radiation.
- Imaging of the lungs: If a pulmonary embolism is suspected, a specialized chest scan is used, chosen to keep radiation exposure low.
- Clinical assessment: Standard blood tests used outside pregnancy are less reliable, so the diagnosis relies heavily on imaging and the overall picture.
Treatment
Confirmed clots are treated with blood thinners (anticoagulants) chosen to be safe during pregnancy.
- Low molecular weight heparin: The preferred treatment in pregnancy, given by injection, because it does not cross the placenta.
- Avoiding certain drugs: Some oral blood thinners are not used during pregnancy because they can harm the developing baby.
- Duration: Treatment usually continues for the rest of the pregnancy and for a period after delivery, when the risk remains high.
- Delivery planning: Anticoagulation is carefully timed around labor and delivery to balance clotting and bleeding risks.
For people at high risk, preventive (lower-dose) heparin may be given during pregnancy or after delivery even without a current clot.
Prevention
- Stay active and avoid long periods of immobility; move and stretch the legs regularly
- Drink enough fluids, especially during travel
- Wear compression stockings if advised
- Tell your care team about any personal or family history of clots so risk can be assessed
- Take preventive blood thinners or follow after-delivery measures if recommended
When to See a Doctor
Contact your care team promptly if you notice swelling, pain, warmth, or redness in one leg during or after pregnancy. Call emergency services immediately for signs of a clot in the lungs:
- Sudden shortness of breath
- Chest pain, especially when breathing in
- A fast or pounding heartbeat
- Coughing up blood
- Fainting or feeling about to faint
These symptoms can be life-threatening and require emergency care without delay.
Frequently Asked Questions
Why does pregnancy increase the risk of blood clots?
Pregnancy hormones increase clotting proteins in the blood, the growing uterus slows blood flow in the leg and pelvic veins, and delivery adds further risk. Together these raise the chance of clots during pregnancy and the weeks after birth.
When is the clot risk highest in pregnancy?
The risk is increased throughout pregnancy but is highest in the first weeks after delivery, especially after a cesarean section. This is why preventive measures and watchfulness continue into the postpartum period.
What are the warning signs of a clot in pregnancy?
Swelling, pain, warmth, or redness in one leg can signal a deep vein clot. Sudden breathlessness, chest pain when breathing, a racing heart, or coughing up blood can mean a clot in the lungs and require emergency care.
Are blood thinners safe during pregnancy?
Low molecular weight heparin is the preferred blood thinner in pregnancy because it does not cross the placenta and is considered safe. Some oral blood thinners are avoided because they can harm the developing baby, so treatment is chosen carefully.
How can blood clots be prevented during pregnancy?
Staying active, avoiding long periods of sitting, drinking enough fluids, and wearing compression stockings if advised all help. People at higher risk may be given preventive heparin during pregnancy or after delivery.
References
- Centers for Disease Control and Prevention (CDC). Venous thromboembolism in pregnancy.
- American College of Obstetricians and Gynecologists (ACOG). Thromboembolism in pregnancy.
- MedlinePlus, U.S. National Library of Medicine. Deep vein thrombosis.