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Labor & postpartum Medical emergency

Blood Clots in Pregnancy

Also known as Venous thromboembolism, VTE, Deep vein thrombosis (DVT), Pulmonary embolism (PE). Any time in pregnancy, with the highest risk in the first 6 weeks after birth.

A blood clot in a deep vein, usually in the leg, is one of pregnancy's quieter dangers. Pregnancy and the weeks right after birth make your blood clot more readily, a change meant to protect you from bleeding at delivery that also raises the odds of a clot forming where it should not. Most start in a leg vein (a deep vein thrombosis, or DVT), causing a swollen, painful, warm leg, usually on the left. The serious worry is that a piece breaks free and lodges in the lungs (a pulmonary embolism, or PE), which can be life-threatening and is one of the leading causes of maternal death. The reassuring part: clots are uncommon, the warning signs are learnable, and blood-thinning injections treat them well when they start early.

Know the warning signs When to call a provider
How common
About 1 to 2 in 1,000 pregnancies
Uncommon, but pregnancy raises the risk about fivefold.
When
Any time, highest after birth
Risk runs through pregnancy and the first 6 weeks postpartum.
Urgency
Can be an emergency
A leg clot means call today; chest pain or breathlessness means call 911.
Outlook
Good with early treatment
Blood-thinning injections treat it safely and effectively.

This can be a medical emergency. These can mean a clot has reached the lungs (a pulmonary embolism) and are a 911 emergency: sudden shortness of breath or difficulty breathing If this happens, go to the ER or call 911 right away.

Understanding it

What is blood clots in pregnancy?

A blood clot in pregnancy usually means a deep vein thrombosis, a clot in one of the large deep veins of the leg or pelvis. The danger is that part of it can break loose and travel to the lungs, a pulmonary embolism, which is far more serious. Together these are called venous thromboembolism, or VTE, and they affect roughly 1 to 2 in 1,000 pregnancies.

Pregnancy tips the body toward clotting. Your blood is built to clot more readily so you lose less at delivery, the growing uterus presses on the veins that drain your legs and pelvis, and you tend to move less, so blood pools. Add the vessel injury that comes with birth, especially a cesarean, and the weeks around delivery become the highest-risk window of all.

A leg clot on its own is very treatable, but a pulmonary embolism can be sudden and fatal, which is why VTE remains one of the leading causes of death in pregnancy and the weeks after. About 1 in 10 pregnancy-related deaths in the US are caused by a clot in the lungs. Nearly all of that risk is preventable and treatable when a clot is caught early.

Knowing the signs is the single most useful thing you can do. A painful, swollen, warm leg, usually on one side, needs a same-day call and an ultrasound. Chest pain, breathlessness, or coughing up blood is a 911 emergency. Treatment is a blood-thinning injection you can learn to give yourself, and it protects both you and your baby.

Symptoms

What are the symptoms?

A blood clot usually shows up first in one leg, and those signs deserve a same-day call. If a clot reaches the lungs, the signs are different and far more urgent. Learning both lists is what keeps a leg clot from becoming a lung emergency.

Early signs

  • Swelling in one leg, the whole leg or just the calf (swelling in both legs is usually just normal pregnancy)
  • Pain, tenderness, or a cramping ache in the leg, often in the calf and often worse when you stand or walk
  • Warmth over the sore area
  • Skin that looks red or discolored, or a leg that feels heavy and tight
  • It most often affects one leg, and more often the left

Emergency signs — call 911

  • These can mean a clot has reached the lungs (a pulmonary embolism) and are a 911 emergency: sudden shortness of breath or difficulty breathing
  • Chest pain or tightness, often sharper when you breathe in or cough
  • Coughing up blood
  • A fast or irregular heartbeat, feeling lightheaded, or fainting
  • Suddenly feeling very unwell, or collapsing

Why it matters

Risks to you and baby

Pulmonary embolism

The chief danger is that part of a leg or pelvic clot breaks off and lodges in the lungs. A pulmonary embolism can strike suddenly and be life-threatening, and it is one of the leading causes of maternal death. This is exactly why a suspected leg clot is treated the same day and why chest or breathing symptoms are a 911 call.

A clot that grows or returns

Untreated, a clot can extend up the leg or throw off further pieces to the lungs, and the tendency that caused it does not vanish at delivery. Blood thinners stop the clot from growing while your body reabsorbs it and guard against a new one, which is why treatment continues for months.

Lasting leg trouble (post-thrombotic syndrome)

A deep leg clot can damage the vein's valves, leaving some people with long-term swelling, aching, heaviness, or skin changes in that leg. Prompt treatment and, later, graduated compression stockings lower the chance of it.

Your baby

The clot itself rarely reaches or harms your baby, and the standard treatment, low-molecular-weight heparin, does not cross the placenta, so it is safe in pregnancy. The real risk to your baby is indirect, through a mother who becomes critically ill from a large embolism. Treating the clot protects you both.

Bleeding from blood thinners

Anticoagulants carry a small risk of bleeding, which matters most around delivery. Your team plans the timing of your injections and your birth carefully so you stay protected from clots without bleeding when it counts.

How it's found

How is it diagnosed?

No blood test reliably rules a clot in or out during pregnancy, so diagnosis rests on imaging: an ultrasound of the leg for a suspected DVT, and a lung scan for a suspected PE. If a clot is strongly suspected, treatment usually starts before the scan confirms it.

Compression (duplex) ultrasound of the leg

A painless scan that presses on the leg veins and watches blood flow to reveal a deep vein clot. It is the first test when a DVT is suspected and is safe in pregnancy. A negative scan with low suspicion may be repeated in a few days to be sure.

CT pulmonary angiogram (CTPA) or V/Q scan

When a pulmonary embolism is suspected, one of these imaging tests looks for a clot in the lung's blood vessels. Both are considered safe in pregnancy, and your team picks the better one for your situation, often after a chest X-ray.

D-dimer blood test, used with caution

This clotting marker rises naturally as pregnancy advances, so a high result does not mean a clot and a normal one cannot be trusted to rule one out. Routine D-dimer testing is not recommended for diagnosing VTE in pregnancy, unlike outside pregnancy.

Treatment while you wait

If a clot is strongly suspected and delivery is not imminent, blood-thinning injections are usually started right away and stopped only if the scans come back clear, because the risk of waiting outweighs the risk of a few doses.

Testing is arranged urgently, the same day, whenever DVT or PE is suspected, at any point in pregnancy or in the weeks after birth.

Treatment

How is it managed?

Treatment is a blood thinner that stops the clot from growing, lets your body dissolve it, and prevents new ones. In pregnancy that means heparin injections, not the tablets used outside pregnancy, and treatment runs for months, well past your baby's birth.

Treatment paths

Low-molecular-weight heparin, given as a once- or twice-daily injection under the skin, is the mainstay, and many people learn to give it themselves. The dose is based on your weight, and routine blood monitoring is usually not needed. Graduated compression stockings and staying mobile support the leg while the clot heals.

Medication

Low-molecular-weight heparin such as enoxaparin or dalteparin is preferred because it is effective, predictable, and does not cross the placenta. Warfarin is avoided in pregnancy because it can harm the baby, and the newer clot-preventing tablets (DOACs) are not used because their safety in pregnancy is not established. After birth, some people switch to warfarin, which is safe while breastfeeding.

Monitoring

Treatment continues for the rest of your pregnancy and for at least 6 weeks after birth, a minimum of 3 months in total. Because the postpartum weeks carry the highest risk, the injections do not stop at delivery. Your team reviews the plan and watches for any sign of a new or growing clot.

Can it recur?

Having had a clot is one of the strongest risk factors for another, so a previous VTE usually means preventive blood-thinner injections through any future pregnancy and the 6 weeks after. The recurrence risk in a later pregnancy without prevention is on the order of several percent. Tell your provider your history as early as possible so a plan is ready from the start.

What you can do

Can it be prevented?

  • Get a clot-risk assessment early and after birth

    At your first visit and again after delivery, your team weighs your risk factors. If they add up, preventive low-molecular-weight heparin injections sharply lower your chance of a clot. Most pregnancy clots occur in people who have an identifiable risk factor, so this review is where much of the prevention happens.

  • Keep moving, and stay hydrated

    Stay as active as you comfortably can, avoid long stretches of sitting or bed rest, and move your legs and feet on long journeys. Drink enough fluids. If you are on bed rest, recovering from surgery, or admitted to hospital, ask what is being done to prevent clots.

  • Use compression stockings if advised, and know your history

    Graduated compression stockings help blood return from the legs and may be recommended if you are at higher risk or during travel. Tell your provider about any previous clot, known clotting disorder, or family history early, since these change the plan.

Who is more at risk

Risk factors

A previous blood clot or a known clotting disorder
A personal history of DVT or PE is the single strongest risk factor, and inherited or acquired thrombophilias (such as factor V Leiden) tip the blood toward clotting. Either usually means preventive injections this pregnancy.
About 1 in 5 people in the US have some form of thrombophilia
The weeks around and after delivery
Birth injures blood vessels and sets off clotting, and a cesarean adds surgery and reduced movement on top. The first weeks postpartum are the highest-risk window of the entire pregnancy.
Immobility and being unwell
Long periods of bed rest, hospital admission, recovery from surgery, a long journey, or a serious illness all slow blood flow in the legs and raise the risk.
Body weight and age
Obesity and being 35 or older each independently increase the risk, and they add up alongside other factors.
A demanding pregnancy
Carrying twins or more, conceiving through IVF, severe morning sickness with dehydration (hyperemesis), preeclampsia, and heavy bleeding at delivery all add to the risk.
Twin and IVF pregnancies each carry a severalfold higher risk

Do not wait

When to call your provider or 911

  • Call 911 or go to the emergency room now for chest pain or tightness, shortness of breath, coughing up blood, a racing or irregular heartbeat, fainting, or suddenly feeling very unwell. These can mean a clot in the lungs.
  • Call your provider or maternity unit the same day for pain, swelling, warmth, or redness in one leg, especially the calf, even if it seems mild.
  • If you are on blood-thinning injections, call for unusual bleeding or bruising, or if you miss a dose, and check in before any procedure, dental work, or travel.
  • Report a previous blood clot, a known clotting disorder, or a strong family history at your first prenatal visit, so a prevention plan can be made early.
  • Keep watching for leg and breathing symptoms in the days and weeks after birth, since the risk is actually highest then, and call promptly if any appear.

Talking to your team

Questions to ask your provider

  • Based on my history, what is my risk of a blood clot, and do I need preventive injections during this pregnancy?
  • Which warning signs in my leg or chest should make me call you, and which mean I should call 911?
  • If I need blood thinners, will I give the injections myself, and how do you decide the dose?
  • How will my treatment be managed around my labor and delivery?
  • Can I still have an epidural, and how long before it do I need to stop my injections?
  • How long will I need to stay on treatment after my baby is born?
  • Should I be doing anything now, like wearing compression stockings, staying active, or taking care on long trips?

Keep reading

More on blood clots in pregnancy

All pregnancy guides articles

Good to Know

Blood Clots in Pregnancy FAQs

Common questions about blood clots in pregnancy, answered.

Is a blood clot in pregnancy really that serious?

A clot in a leg vein is very treatable, and most people do well. The danger is a piece breaking off and traveling to the lungs, a pulmonary embolism, which can be sudden and life-threatening and is one of the leading causes of maternal death. That is why leg symptoms get a same-day call and chest or breathing symptoms are a 911 emergency. Caught early, it is treated safely.

Where do these clots usually form?

Almost always in the deep veins of a leg or the pelvis, and more often in the left leg than the right, partly because of how the pregnant uterus presses on the veins. A clot there is a deep vein thrombosis; the worry is that it can travel to the lungs and become a pulmonary embolism.

My ankles are swollen. How do I know if it is a clot?

Mild swelling in both feet and ankles is a normal part of pregnancy. A clot is different: it usually affects one leg, and that leg tends to be painful, warm, and sometimes red, with swelling that can reach the calf or thigh. When it is one-sided and sore, do not wait, call the same day.

Are blood thinners safe for my baby?

Yes. The standard treatment, low-molecular-weight heparin, does not cross the placenta, so it does not reach or harm your baby, and it has a long track record in pregnancy. It is the anticoagulant of choice precisely because it treats you effectively while keeping your baby safe.

Why injections instead of pills?

The blood-thinning tablets used outside pregnancy are not safe here. Warfarin crosses the placenta and can harm the baby, and the newer tablets called DOACs have not been proven safe in pregnancy. Heparin injections stay in your bloodstream and do not reach the baby, which makes them the right choice.

Can I still have a normal birth and an epidural?

Usually yes. A clot is not on its own a reason for a cesarean. Your birth is simply planned around your injections: you stop them when labor starts, or about 24 hours before a planned delivery, and an epidural or spinal is timed to a safe gap after your last dose. Your team walks you through it.

How long will I have to stay on treatment?

Longer than many expect. Treatment continues for the rest of your pregnancy and for at least 6 weeks after birth, and for a minimum of 3 months in total. The weeks right after delivery are the highest-risk time, so the injections deliberately do not stop when your baby arrives.

Will it happen again in my next pregnancy?

Having had a clot is one of the strongest risk factors for another, so most people who have had a VTE are offered preventive heparin injections throughout a future pregnancy and for 6 weeks after. Tell your provider your history as early as you can so the plan is ready from day one.

Medically Reviewed · Updated

Reviewed by Dr. Grace Lin, MD, FACOG · OB-GYN

Obstetrician-gynecologist focused on reproductive and sexual health for women: pregnancy, BV, yeast, trichomoniasis and HPV/cervical screening. Our editorial guidelines →

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