Reducing the Risk of Venous Thromboembolism during Pregnancy and the Puerperium

Key Recommendations

• VTE remains a leading direct cause of maternal death in the UK
• All women should undergo documented VTE risk assessment at booking, on admission, and postnatally
• Thromboprophylaxis with LMWH is first-line when indicated
• Risk assessment should be repeated if clinical circumstances change (e.g. admission, surgery, immobilisation)

Risk Factors

Pre-existing

• Previous VTE (highest risk — 25% recurrence)
• Known thrombophilia (Factor V Leiden, Prothrombin gene mutation, Antithrombin deficiency, Protein C/S deficiency, Antiphospholipid syndrome)
• BMI >30 kg/m2
• Age >35 years
• Parity ≥3
• Smoking
• Significant medical comorbidity (SLE, cancer, heart failure, inflammatory conditions, nephrotic syndrome, sickle cell disease)
• Paraplegia
• Family history of VTE

Obstetric

• Multiple pregnancy
• Pre-eclampsia
• Caesarean section (especially emergency)
• Prolonged labour (>24 hours)
• PPH >1 litre or blood transfusion
• Preterm birth
• Stillbirth
• Hyperemesis, dehydration
• OHSS (ovarian hyperstimulation syndrome)

Transient

• Surgical procedure in pregnancy or puerperium
• Immobilisation (>3 days bedrest, long-distance travel >4 hours)
• Systemic infection
• Admission to hospital

Risk Assessment and Thromboprophylaxis

Antenatal

• 4 or more risk factors: consider LMWH from 1st trimester
• 3 risk factors: consider LMWH from 28 weeks
• Previous VTE: LMWH from 1st trimester (throughout pregnancy)
• Antithrombin deficiency or antiphospholipid syndrome with previous VTE: higher-dose LMWH, consider specialist input

Postnatal

• All women post-caesarean: minimum 10 days LMWH (unless low risk and mobilising well)
• Previous VTE: 6 weeks postnatal LMWH
• 2 or more current risk factors: 10 days postnatal LMWH
• Emergency caesarean: consider extended prophylaxis

LMWH Dosing

• High-risk (previous VTE): higher prophylactic or intermediate dose
• Delivery: omit LMWH dose when in established labour or before planned delivery
• Regional anaesthesia: minimum 12 hours after prophylactic LMWH dose, 24 hours after therapeutic dose

Diagnosis of VTE in Pregnancy

• D-dimer physiologically elevated in pregnancy — less useful for exclusion
• Suspected DVT: compression duplex USS (can be repeated if initially negative)
• Suspected PE: CTPA (first-line) or V/Q scan
• Start LMWH while awaiting investigations — do not delay treatment

Important Facts for MRCOG

• VTE is a leading cause of direct maternal death in the UK
• All pregnant women need documented VTE risk assessment at booking
• LMWH is first-line for thromboprophylaxis (NOT warfarin, which is teratogenic)
• Warfarin: crosses placenta, causes warfarin embryopathy (nasal hypoplasia, stippled epiphyses) — used only in exceptional circumstances (e.g. mechanical heart valves)
• LMWH does NOT cross the placenta and is safe in breastfeeding
• Post-caesarean: minimum 10 days LMWH for all (unless very low risk)
• Previous VTE: LMWH throughout pregnancy + 6 weeks postpartum
• D-dimer is NOT reliable for VTE exclusion in pregnancy

Source: RCOG Green-top Guideline No. 37a (2015 (reviewed 2020))

Read the original on rcog.org.uk

Clinically reviewed by NHS obstetricians and gynaecologists · Source last updated 2015 (reviewed 2020)

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