This information is for general guidance only.

It does not replace advice from your midwife, GP or haematology team. Read more about our approach.

DVT in pregnancy: blood clot risks, symptoms and prevention

What is DVT and why is pregnancy a risk?

Deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, usually in the lower leg or thigh. During pregnancy, the risk of DVT is 5 times higher than in non-pregnant women of the same age. This is because pregnancy causes natural changes to the blood's clotting system to prepare for the blood loss of birth, a beneficial change that can occasionally cause problems.

The risk continues for up to 6 weeks after birth and is highest in the first week after delivery. Pulmonary embolism (a clot in the lungs) remains one of the leading causes of maternal death in the UK, which is why awareness and prevention are so important. Staying active prevents blood clots is one of the most effective steps you can take, and DVT risk after caesarean is particularly elevated in the first week. See also our page on other pregnancy complications to know about.

How common is DVT in pregnancy?

5x

higher risk in pregnancy vs non-pregnant

1 in 1,000

pregnant women develops a DVT

Week 1

after birth, risk is highest

Most

DVTs are preventable with precautions

Symptoms: know what to look for

DVT symptoms (usually in ONE leg)

  • Pain or tenderness in the calf or thigh, often worse when walking
  • Swelling of one leg, noticeably more than the other
  • Warm skin in the affected area
  • Redness, particularly at the back of the leg below the knee
  • A heavy aching sensation

Swollen ankles and feet are common in normal pregnancy. The concern is when only ONE leg is affected, or when pain and warmth accompany swelling.

Risk factors

High risk

May need preventive heparin throughout pregnancy.

  • Previous DVT or pulmonary embolism
  • Thrombophilia (inherited clotting disorder: factor V Leiden, protein C/S deficiency, antiphospholipid syndrome)
  • Antiphospholipid syndrome

Moderate risk

Preventive measures strongly recommended.

  • BMI over 30 before pregnancy
  • Age 35 or over
  • Family history of blood clots (parent or sibling)
  • Multiple pregnancy (twins or more)
  • Pre-eclampsia
  • Caesarean section (especially emergency)
  • Prolonged labour (over 24 hours)
  • Significant blood loss at delivery
  • Severe infection or illness during pregnancy
  • Dehydration
  • Immobility (bed rest, long travel)
  • Varicose veins (large, painful, above the knee)
  • 3 or more previous pregnancies
  • IVF treatment

Preventing DVT in pregnancy

Stay active

Regular walking is one of the most effective preventive measures. Aim for 30 minutes of gentle activity a day if possible. If on bed rest, flex and rotate your ankles and do gentle leg exercises regularly.

Stay hydrated

Aim for 6 to 8 glasses of water a day. Dehydration thickens the blood and increases clot risk.

Compression stockings

Graduated compression stockings (class 1 or 2) improve circulation. Recommended for women with risk factors and for all women during long-distance travel. Available from pharmacies without prescription.

Heparin (LMWH) injections

Low molecular weight heparin (enoxaparin, tinzaparin) is used to prevent and treat DVT in pregnancy. Safe for baby, does not cross the placenta. Self-injected under the skin. Prescribed at booking if you have significant risk factors, and often continued for 6 weeks after birth.

After birth

Risk remains elevated for up to 6 weeks after delivery. Continue heparin if prescribed until the course is complete. Stay mobile as soon as possible, even after a caesarean. Wear compression stockings if prescribed.

Travel and DVT

✈️ Flying

  • Flights over 4 hours: wear compression stockings, walk the aisle every 30 minutes, stay well hydrated, avoid alcohol.
  • After 28 weeks, your airline may require a letter from your GP or midwife. Check before booking.
  • After 37 weeks (or 32 weeks with twins), most airlines will not allow you to fly.

🚗 Car travel

  • Stop every 1 to 2 hours for a walk and stretch.
  • Keep windows slightly open for fresh air.
  • Seatbelt: lap strap under the bump, not across it.
  • Compression stockings are recommended for journeys over 4 hours.

⛴️ Ferries

Most will not carry passengers beyond 32 weeks on high-speed crossings, or 32 to 36 weeks on standard crossings. Check the operator's policy.

Diagnosis

  • Compression ultrasound scan of the leg veins is the standard investigation. Usually same day or urgent referral.
  • Blood tests including D-dimer may be used but are less reliable in pregnancy (D-dimer is often raised anyway).
  • If pulmonary embolism is suspected: chest X-ray, CT pulmonary angiogram (CTPA) or V/Q scan.
  • Do not delay seeking assessment because you are worried about radiation. The benefit of diagnosis outweighs the very small risk.

Treatment

  • LMWH injections are the standard treatment. Safe throughout pregnancy and while breastfeeding.
  • Usually continued for the rest of the pregnancy and for at least 6 weeks after birth (minimum 3 months of treatment in total).
  • Warfarin is NOT used in pregnancy (crosses the placenta). It may be used after birth.
  • Direct oral anticoagulants (DOACs such as rivaroxaban) are NOT recommended in pregnancy or while breastfeeding.
  • No routine INR blood tests are needed with LMWH, unlike warfarin. Anti-Xa levels may occasionally be checked.

After birth

Tell your birth team you are on heparin. It affects the timing of epidurals and spinal blocks, as a gap is needed between the last heparin dose and regional anaesthesia.

Continue heparin injections after birth as prescribed. Do not stop early without medical advice.

At your postnatal check (around 6 weeks), you will discuss whether to continue or stop. Warfarin or DOACs may be considered after birth.

Related guides and tools

Staying active in pregnancy→ DVT prevention after caesarean→ Discussing your risk at booking→ Other pregnancy complications→

A note from our team

This guide reflects NHS UK, NICE and RCOG guidance on thromboembolism in pregnancy. Your midwife and obstetric team will tailor advice to your risk factors. Read more about us.

Frequently asked questions

Is DVT common in pregnancy?
It is uncommon, but the risk is around 5 times higher than in non-pregnant women of the same age. Roughly 1 in 1,000 pregnant women develops a DVT. The risk is highest in the third trimester and in the first week after birth, and remains elevated for up to 6 weeks postnatally.
What does a DVT feel like in pregnancy?
Usually pain, swelling and tenderness in one leg, especially the calf. The skin may feel warm or look red, often behind the knee. A heavy aching sensation is common. Swollen ankles and feet are normal in pregnancy, so the concern is when only one leg is affected or when pain and warmth are present alongside swelling.
Is heparin safe in pregnancy?
Yes. Low molecular weight heparin (LMWH) is the treatment of choice for preventing and treating DVT in pregnancy. It does not cross the placenta, so it does not affect the baby. It is given by subcutaneous injection. Your midwife or pharmacist will teach you how to self-inject.
Can I fly when pregnant?
Most airlines allow flying until 36 to 37 weeks (32 weeks for twins). For flights over 4 hours, wear compression stockings, walk the aisle every 30 minutes, stay hydrated and avoid alcohol. After 28 weeks, many airlines require a letter from your GP or midwife. Always check the airline's policy before booking.
How do I prevent blood clots in pregnancy?
Stay active with regular walking, stay well hydrated, wear graduated compression stockings if recommended or during long travel, and take heparin injections if prescribed. After birth, get moving as soon as safely possible, even after a caesarean. If you have risk factors, your midwife will discuss extra steps at your booking appointment.
What is a pulmonary embolism and how is it different from DVT?
A DVT is a clot in a deep vein, usually in the leg. A pulmonary embolism (PE) is when a clot breaks off and travels to the lungs. PE is a medical emergency and can cause sudden shortness of breath, chest pain, rapid heart rate and coughing up blood. Call 999 immediately if you have these symptoms.
How long after birth am I at risk of DVT?
The risk remains higher than usual for up to 6 weeks after birth, and is highest in the first week. If you have been prescribed heparin, continue the full course as directed, including after you go home. Stay mobile, keep hydrated, and watch for the warning signs even weeks after delivery.