Venous Thromboembolism (VTE) in Pregnancy

Summary

 VTE is a leading cause of maternal death, with risk highest postpartum. Prompt recognition, imaging-based diagnosis, and LMWH treatment are key, while risk assessment and prophylaxis remain essential for prevention.

Definition

Venous thromboembolism (VTE) encompasses deep vein thrombosis (DVT) and pulmonary embolism (PE). It is a major cause of maternal morbidity and mortality, accounting for approximately one-third of maternal deaths in the UK. Pregnancy confers a 4–5-fold increased risk of VTE, largely due to physiological changes in haemostasis, including increased fibrinogen levels, reduced protein S activity, and venous stasis. The risk escalates as pregnancy advances, peaking in the postpartum period, particularly in the first week after delivery.

Risk Factors

Pregnancy increases VTE risk through Virchow’s triad:

• Stasis: uterine compression, especially May-Thurner syndrome (left iliac vein compression), explains why ~90% of DVTs occur on the left and 70% in iliofemoral veins.

• Hypercoagulability: raised clotting factors (V, VII, VIII, X, vWF, fibrinogen), resistance to protein C, reduced protein S, and increased fibrinolytic inhibitors.

• Endothelial injury: uterine compression and vascular trauma at delivery.

Additional risk factors include:

• Pre-existing: thrombophilia, previous VTE, obesity, age >35, parity >3, smoking, malignancy.

• Obstetric: multiple pregnancy, pre-eclampsia, caesarean, prolonged labour, stillbirth, preterm birth, PPH.

• Transient: dehydration, ovarian hyperstimulation, infection, surgery, immobility, long-distance travel.

Clinical Features

Deep Vein Thrombosis (DVT)

• Typical symptoms: unilateral leg pain and swelling (most often left-sided).

• Other features: pitting oedema, tenderness, pyrexia, or prominent superficial veins.

• Pathophysiology: Proximal DVTs are more common in pregnancy due to uterine compression of the left iliac vein.

• Differential diagnosis: cellulitis, ruptured Baker’s cyst, superficial thrombophlebitis (treated as DVT if near deep venous junction), or physiological oedema of pregnancy.

Pulmonary Embolism (PE)

• Symptoms: sudden-onset dyspnoea, pleuritic chest pain, cough, rarely haemoptysis.

• Signs: tachycardia, tachypnoea, pyrexia, occasionally raised JVP, pleural rub, or effusion.

• Differential diagnosis: pneumonia, myocardial infarction, peripartum cardiomyopathy, amniotic fluid embolism.
  

Investigations

• Blood tests: FBC, U&Es, LFTs, coagulation profile (required prior to anticoagulation).

• D-dimer: not useful in pregnancy due to physiologic elevation.

For suspected DVT:

• First-line: compression duplex ultrasound.

• If negative but suspicion persists: repeat after 1 week (with interim anticoagulation).

For suspected PE:

• Initial: ECG, chest X-ray ± ABG.

• Definitive: CTPA or V/Q scan (counsel regarding radiation risks: V/Q scan → higher risk of childhood cancer, lower breast cancer risk).

• If DVT is confirmed on ultrasound, chest imaging may be avoided.

Management

Anticoagulation

• Initial treatment: start low-molecular-weight heparin (LMWH) immediately, pending definitive diagnosis. Dose adjusted to booking weight.

• Duration: throughout pregnancy and for 6–12 weeks postpartum (minimum 3–6 months total).

• Delivery considerations: withhold LMWH 24 hours before induction/caesarean; avoid in spontaneous labour.

• Alternatives: unfractionated heparin (useful near delivery as it can be stopped 6 hours before labour).

• Contraindicated: warfarin (teratogenic, risk of fetal haemorrhage). DOACs not recommended in pregnancy; may be considered postpartum if not breastfeeding.

• SO, LMWH is the treatment of choice; warfarin and DOACs are contraindicated during pregnancy.

Severe PE

• ABCDE resuscitation.

• Consider IV unfractionated heparin or systemic thrombolysis in massive PE with haemodynamic instability.

Prophylaxis

• Risk assessment: should be performed at booking, intrapartum, and postpartum.

• Indications for antenatal thromboprophylaxis (UK guidelines):

  • ≥4 risk factors in 1st–2nd trimester

  • ≥3 risk factors in 3rd trimester

  • ≥2 risk factors postpartum

• Caesarean section: 10-day course of LMWH recommended (especially after emergency procedures).

• Previous VTE / thrombophilia:

• Provoked VTE (major surgery): LMWH from 28 weeks.

• Unprovoked/other VTE: LMWH throughout pregnancy and postpartum.

• Antithrombin deficiency / antiphospholipid syndrome: high-dose LMWH, often in consultation with haematology.