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Anticoagulant — VTE Treatment and Prophylaxis in Pregnancy Pregnancy: Safe in pregnancy — drug of choice for VTE in pregnancy

Low Molecular Weight Heparin (Pregnancy VTE)

Brand names: Tinzaparin (Innohep), Enoxaparin (Clexane), Dalteparin (Fragmin)

Adult dose

Dose: Treatment: 175 units/kg (tinzaparin) or 1 mg/kg twice daily (enoxaparin) SC. Prophylaxis: 4500 units (tinzaparin) or 40 mg (enoxaparin) SC once daily
Route: Subcutaneous injection
Frequency: Once or twice daily depending on indication and agent
Max: Weight-adjusted; dose increases during pregnancy as weight and volume of distribution increase
RCOG Green-top 37a: LMWH is treatment of choice for VTE in pregnancy — warfarin teratogenic, DOACs contraindicated. Dose by booking weight; reassess at 20 and 34 weeks

Paediatric dose

Dose: Not applicable N/A/kg
Route: N/A
Frequency: N/A
Max: N/A
Maternal anticoagulation

Dose adjustments

Renal

Anti-Xa monitoring required in renal impairment — accumulation risk; UFH preferred if eGFR under 30

Hepatic

Use with caution

Paediatric weight-based calculator

Maternal anticoagulation

Clinical pearls

  • LMWH does not cross the placenta — safe for fetus; preferred anticoagulant throughout pregnancy and postnatally (6 weeks minimum after VTE, 10 days minimum after delivery for prophylaxis)
  • Regional anaesthesia timing: stop prophylactic LMWH 12 hours before epidural; therapeutic LMWH 24 hours before — coordinate with anaesthetic team for planned delivery
  • Anti-Xa monitoring in pregnancy: peak levels (4 hours post-dose) target 0.6-1.0 units/mL (treatment twice daily) — recommended in extremes of weight (under 50 kg or above 90 kg)
  • Antiphospholipid syndrome with prior thrombosis: LMWH + aspirin 75 mg throughout pregnancy — reduces recurrent pregnancy loss and maternal thrombosis
  • Reversal: protamine sulfate partially reverses LMWH (60-70%) — useful for emergency delivery; 1 mg protamine per 100 anti-Xa units given in preceding 8 hours

Contraindications

  • Active major bleeding
  • HIT
  • Epidural/spinal within timing window

Side effects

  • Bleeding
  • Injection site bruising and haematoma
  • HIT (rare)
  • Osteoporosis (prolonged use)
  • Hyperkalaemia

Interactions

  • Aspirin (additive bleeding — but combination used in antiphospholipid syndrome)
  • NSAIDs (increased bleeding)

Monitoring

  • Anti-Xa levels (peak 4 hours post-dose — therapeutic: 0.6-1.0 units/mL)
  • Platelet count (HIT surveillance)
  • Weight at each antenatal visit (dose adjustment)
  • Signs of bleeding

Reference: BNFc; BNF 90; RCOG Green-top Guideline 37a (VTE in Pregnancy 2015); NICE NG201 (VTE in Pregnancy). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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