Blood Clots in Pregnancy and After Birth: Signs, Prevention and Treatment
Key message: Pregnancy and especially the first weeks after birth increase the risk of venous thrombosis, although it…
Key message: Pregnancy and especially the first weeks after birth increase the risk of venous thrombosis, although it remains uncommon. A clot in a leg can travel to the lungs, so one-sided leg symptoms or sudden breathing symptoms need immediate assessment.
Get urgent help: Call emergency services for sudden unexplained breathlessness, chest pain or tightness, coughing blood, collapse, severe dizziness or a very fast heartbeat with feeling unwell. Seek same-day urgent assessment for pain, tenderness, warmth, redness or swelling mainly in one leg.
What are DVT and pulmonary embolism?
Deep-vein thrombosis (DVT) is a clot in a deep vein, often in the leg or pelvis. Pulmonary embolism (PE) occurs when part of a clot travels to the lungs and can be life-threatening.
Pregnancy clots can occur at any gestation, and risk is highest soon after birth.
Which factors increase risk?
- Previous VTE or a significant thrombophilia.
- Caesarean birth, major bleeding, infection or surgery.
- Reduced mobility, hospital admission or long travel.
- Higher BMI, smoking, age and multiple pregnancy.
- Pre-eclampsia, hyperemesis, severe medical disease or ovarian hyperstimulation.
- Family history and combined risk factors.
When is risk assessed?
Risk should be assessed early in pregnancy, during hospital admissions, when circumstances change and again after birth. A score alone does not replace clinical judgement.
The recommendation may change after emergency caesarean, haemorrhage, infection or prolonged immobility.
How is DVT diagnosed?
- Clinical assessment and compression ultrasound of the leg.
- Repeat imaging when suspicion remains despite a negative initial scan.
- Blood tests as part of the assessment, although D-dimer alone is not a reliable rule-out test in pregnancy.
- No delay in treatment when clinical suspicion is high and imaging is being arranged.
How is suspected PE investigated?
Assessment may include chest X-ray, lung scanning or CT pulmonary angiography depending on symptoms, chest findings and local expertise. The small radiation risks are weighed against the serious risk of missing a PE.
Pregnancy should not prevent appropriate emergency imaging.
How are clots treated?
Low-molecular-weight heparin injections are commonly used in pregnancy because they do not cross the placenta. Treatment duration includes pregnancy and at least part of the postpartum period, with a minimum total course according to the diagnosis and guideline.
After birth, heparin or selected oral anticoagulants may be used; breastfeeding compatibility and bleeding risk guide the choice.
How can risk be reduced?
- Remain mobile and hydrated when medically able.
- Use properly fitted compression stockings when advised.
- Take preventive heparin for the exact prescribed duration.
- Plan long journeys and perioperative care.
- Stop smoking and address modifiable risks without blame.
- Know how anticoagulation affects labour, epidural timing and planned procedures.
What if labour starts while taking heparin?
Do not take another dose until speaking to the maternity unit when labour, waters breaking or significant bleeding begins. The team needs the exact medicine, dose and time of the last injection.
Regional anaesthesia timing depends on the anticoagulant dose and interval; never change the schedule independently.
What follow-up is needed?
Follow-up reviews duration, cause, future contraception, future pregnancy prevention and whether thrombophilia testing is indicated after treatment. Not everyone requires a thrombophilia panel.
Persistent breathlessness, leg swelling or post-thrombotic symptoms deserve review.
Frequently asked questions
Can a clot happen in early pregnancy?
Yes. Risk exists throughout pregnancy and is highest after birth.
Is leg swelling normal in pregnancy?
Both legs may swell, but one-sided painful, red or hot swelling needs urgent assessment.
Will heparin harm the baby?
Low-molecular-weight heparin does not cross the placenta.
Can I breastfeed on anticoagulants?
Several options are compatible; the postnatal prescription is chosen individually.
Should everyone take aspirin to prevent a clot?
No. Aspirin does not replace VTE risk assessment or prescribed heparin.
Your next step
Keep the exact anticoagulant name, dose and last-injection time available. Emergency chest symptoms need an ambulance; one-sided leg symptoms need same-day assessment.
Medical and content review: Dr Mohamed Abdelghany, Obstetrics & Gynecology Specialist, MRCOG (UK), MSc Obstetrics & Gynecology – Kasr Al-Ainy, Cairo University.
Last reviewed: 23 August 2026.
This information is for general education and does not replace individual medical assessment. Severe, sudden or concerning symptoms should not wait for a routine appointment.
