Key Facts

Venous thromboembolism in pregnancy encompasses deep vein thrombosis (DVT) and pulmonary embolism (PE). Pregnancy is a prothrombotic state due to Virchow's triad: hypercoagulability, venous stasis, and endothelial injury. VTE remains the leading direct cause of maternal death in the UK.

Epidemiology

• Incidence: 1-2 per 1,000 pregnancies
• Risk is present throughout pregnancy and the puerperium, with highest risk in the first 6 weeks postpartum
• Accounts for approximately 1.13 deaths per 100,000 maternities in the UK (MBRRACE-UK 2020)
• DVT is more common antepartum; PE is more common postpartum
• Left-sided DVT predominates (85%) due to compression of the left common iliac vein by the right iliac artery

Aetiology

• Hypercoagulability: increased levels of factors VII, VIII, X, fibrinogen, von Willebrand factor; decreased protein S; acquired resistance to activated protein C
• Venous stasis: compression of pelvic veins by the gravid uterus; hormonally mediated venodilation
• Endothelial injury: during delivery, particularly caesarean section
• Additional risk factors: previous VTE, known thrombophilia (Factor V Leiden, prothrombin gene mutation, antithrombin deficiency, antiphospholipid syndrome), obesity (BMI >30), immobility, pre-eclampsia, dehydration, long-haul travel

Pathophysiology

• Pregnancy induces a physiological hypercoagulable state to minimise blood loss at delivery
• Venous stasis worsens as the uterus enlarges, compressing the IVC and iliac veins
• Thrombus formation typically begins in the deep veins of the calf or iliofemoral segment
• Embolisation to the pulmonary vasculature causes PE with ventilation-perfusion mismatch and, in severe cases, right ventricular failure

Deep Vein Thrombosis

• Unilateral leg swelling (>2 cm difference in calf circumference)
• Pain and tenderness, particularly in the calf or thigh
• Erythema and warmth
• Left leg affected in 85% of cases
• Symptoms may overlap with normal pregnancy-related leg swelling

Pulmonary Embolism

• Sudden-onset dyspnoea (most common symptom)
• Pleuritic chest pain
• Tachycardia and tachypnoea
• Haemoptysis
• Collapse or cardiac arrest in massive PE

Red Flags

• Sudden-onset dyspnoea with pleuritic chest pain
• Haemodynamic instability (massive PE)
• Oxygen saturations <94%
• Signs of right heart strain
• Unilateral leg swelling with pain at any stage of pregnancy or within 6 weeks postpartum

Bedside

• Oxygen saturations and ABG if PE suspected
• ECG (sinus tachycardia most common; S1Q3T3 pattern, right axis deviation in PE)
• Chest X-ray (to exclude other causes; often normal in PE)
• Leg circumference measurements (>2 cm difference is significant)

Bloods

• FBC, U&Es, LFTs
• Coagulation screen
• D-dimer is NOT reliable in pregnancy (physiologically elevated); do not use to exclude VTE
• Thrombophilia screen (defer to 6 weeks postpartum; not done acutely)

Imaging

• Compression duplex USS: first-line for suspected DVT; sensitivity >95% for proximal DVT
• If USS negative but high clinical suspicion: repeat in 3-7 days or perform MR venography
• CTPA: preferred investigation for PE in pregnancy (RCOG GTG 37b); higher sensitivity and specificity than V/Q scan
• V/Q scan: alternative if CTPA contraindicated; lower radiation dose to maternal breast tissue

Special Tests

• Echocardiography if massive PE (right ventricular dilatation, McConnell's sign)
• MR venography for iliac vein thrombosis if USS equivocal

Non-pharmacological

• Elevate affected leg and apply graduated compression stockings (after excluding arterial disease)
• Early mobilisation once anticoagulated
• Adequate hydration
• Risk assessment using RCOG VTE risk assessment tool at booking, during admission, and postpartum

Pharmacological

• LMWH is the treatment of choice:
  • Enoxaparin 1mg/kg BD (treatment dose) or 1.5mg/kg OD
  • Dalteparin 200 units/kg OD or 100 units/kg BD
  • Tinzaparin 175 units/kg OD
• Continue treatment dose LMWH throughout pregnancy and for at least 6 weeks postpartum (minimum total duration 3 months)
• Switch to unfractionated heparin around delivery if epidural/spinal planned (shorter half-life)
• Warfarin is teratogenic in first trimester (avoid); may be used postpartum (safe in breastfeeding)
• DOACs are contraindicated in pregnancy and breastfeeding
• Thrombolysis (alteplase 50mg IV) for massive PE with haemodynamic compromise

Surgical/Interventional

• Surgical embolectomy or catheter-directed thrombolysis for life-threatening PE unresponsive to medical therapy
• IVC filter in rare cases where anticoagulation is contraindicated and recurrent PE

Referral Criteria

• Immediate referral to obstetric medicine/haematology for confirmed VTE
• Anaesthetic review for delivery planning (timing of LMWH cessation)
• Thrombophilia screening at 6 weeks postpartum
• Postnatal review to determine duration of anticoagulation

• Maternal mortality from PE: approximately 1-2% with treatment
• Case fatality rate for untreated PE: 30%
• Recurrence risk in subsequent pregnancies: 5-12% (higher with thrombophilia)
• Post-thrombotic syndrome develops in 20-50% of DVT cases
• Long-term anticoagulation may be required if recurrent VTE or high-risk thrombophilia
• With appropriate thromboprophylaxis, risk of recurrence is significantly reduced

RCOG VTE Risk Assessment

LMWH Dosing for Thromboprophylaxis (Weight-Based)

Peripartum LMWH Management