Deep Vein Thrombosis in Pregnancy
Pregnancy increases thrombosis risk 4–5 fold — prompt diagnosis and treatment prevent fatal pulmonary embolism.
Overview
Venous thromboembolism (VTE) remains a leading direct cause of maternal death in the UK. Risk is elevated from early pregnancy and peaks in the puerperium. Diagnostic and treatment pathways are pregnancy-specific: D-dimer is unreliable, imaging is preferred, and low molecular weight heparin (LMWH) is the anticoagulant of choice.
Symptoms
- • Unilateral leg swelling, pain, warmth, redness
- • Calf tenderness, increased calf circumference (>2 cm)
- • Lower abdominal pain (iliac vein DVT — more common left side)
- • Symptoms of PE: pleuritic chest pain, breathlessness, tachycardia
Risk factors
- • Previous VTE, thrombophilia
- • Age >35, BMI >30, parity ≥3, smoking
- • Multiple pregnancy, IVF, immobility, long-haul travel
- • Caesarean section (especially emergency), pre-eclampsia
- • Hyperemesis, dehydration, infection, sickle cell disease
Causes
- • Pregnancy-induced hypercoagulability (raised factors VII, VIII, X, fibrinogen)
- • Reduced venous return from gravid uterus
- • Endothelial injury at delivery
🚨 Red flags — seek urgent care
- • Suspected PE — collapse, hypoxia, tachycardia, chest pain
- • Phlegmasia cerulea dolens — massive iliofemoral DVT with cyanotic, painful swollen leg
- • Bilateral leg swelling with abdominal pain — IVC thrombus
When to seek care
- • Any leg swelling, calf pain or sudden breathlessness in pregnancy or up to 6 weeks postpartum — same-day assessment
- • Risk-factor reassessment at booking, antenatally, on admission and postnatally
Diagnosis
- • Do NOT use D-dimer — unreliable in pregnancy
- • Compression duplex ultrasound — first-line for suspected DVT
- • If negative but high suspicion, repeat day 3 and 7 or proceed to MR venography
- • Suspected PE: CXR + bilateral leg ultrasound; if DVT confirmed, treat without further imaging
- • If PE workup needed: V/Q scan or CTPA (informed discussion of fetal vs maternal radiation)
Treatment
- • Therapeutic LMWH (e.g. enoxaparin 1 mg/kg twice daily by booking weight) immediately on clinical suspicion until diagnosis excluded
- • Continue antenatally and for at least 6 weeks postpartum (minimum 3 months total)
- • Avoid DOACs and warfarin (warfarin teratogenic; both excreted in breast milk variably)
- • Switch to warfarin postnatally if preferred (compatible with breastfeeding)
- • Stop LMWH ≥24 hours before planned delivery or regional anaesthesia
- • Graduated compression stocking, mobilisation, hydration
Prevention
- • Risk-assess VTE at every contact (RCOG Green-top 37a)
- • Prophylactic LMWH for high-risk women antenatally and postnatally
- • Early mobilisation, hydration, TED stockings perioperatively
Complications
- • Pulmonary embolism (potentially fatal)
- • Post-thrombotic syndrome
- • Recurrent VTE
- • Heparin-induced thrombocytopenia (rare with LMWH)
- • Bleeding (regional anaesthesia, postpartum haemorrhage)
Prognosis
Excellent with prompt anticoagulation; most women complete the pregnancy safely and deliver healthy babies. Risk of recurrence in future pregnancies is significant — prophylaxis indicated.
Education & self-care
If you have leg swelling, calf pain or sudden breathlessness in pregnancy or the 6 weeks after birth, seek same-day medical assessment.
Frequently asked questions
Can I have an epidural on LMWH?
Yes — but treatment dose must be held for ≥24 hours and prophylactic dose ≥12 hours before insertion.
Is LMWH safe for my baby?
Yes — it does not cross the placenta and is not excreted in clinically relevant amounts in breast milk.
Will I need anticoagulation in future pregnancies?
Usually yes — at least postnatal prophylaxis, often antenatal too.