What is the recommended dose of Low Molecular Weight Heparin (LMWH) for Deep Vein Thrombosis (DVT) prophylaxis in pregnancy?

LMWH Dosing for DVT Prophylaxis in Pregnancy

For DVT prophylaxis during pregnancy, use prophylactic-dose LMWH: enoxaparin 40 mg subcutaneously once daily or dalteparin 5,000 units subcutaneously once daily, with consideration for intermediate-dose regimens (enoxaparin 40 mg every 12 hours or dalteparin 5,000 units every 12 hours) in higher-risk patients. 1

Risk Stratification for Prophylaxis

Antepartum prophylaxis is indicated for pregnant women with specific high-risk features 1:

• Previous unprovoked VTE 1
• Pregnancy or estrogen-related VTE 1
• Homozygous factor V Leiden or prothrombin G20210A mutation 1
• Antiphospholipid antibody syndrome 1

For pregnant women with a single previous VTE associated with a transient risk factor (not pregnancy or estrogen related), antepartum prophylaxis is not recommended 1.

Prophylactic Dosing Regimens

The American College of Chest Physicians defines three prophylactic approaches 1:

Standard Prophylactic-Dose LMWH

• Enoxaparin 40 mg subcutaneously every 24 hours 1, 2
• Dalteparin 5,000 units subcutaneously every 24 hours 1
• Tinzaparin 4,500 units subcutaneously every 24 hours 1
• Nadroparin 2,850 units subcutaneously every 24 hours 1

Note that at extremes of body weight, dose modification may be required 1.

Intermediate-Dose LMWH (for higher-risk scenarios)

• Dalteparin 5,000 units subcutaneously every 12 hours 1
• Enoxaparin 40 mg subcutaneously every 12 hours 1

Dose-Adjusted LMWH (alternative approach)

• LMWH with dose adjustment targeting anti-factor Xa levels of 0.2-0.6 U/mL 1

Key Distinctions: Prophylaxis vs. Treatment

Critical caveat: The dosing above is for prophylaxis only. If a pregnant woman develops acute DVT, therapeutic anticoagulation is required with weight-adjusted dosing 3, 4:

• Enoxaparin 1 mg/kg every 12 hours (therapeutic dose) 3, 2, 4
• Dalteparin 100 units/kg every 12 hours (therapeutic dose) 3

This distinction is essential—prophylactic doses are inadequate for treating established thrombosis 5.

Postpartum Management

All pregnant women with prior VTE should receive postpartum prophylaxis for 6 weeks with 1, 2:

• Prophylactic-dose LMWH (enoxaparin 40 mg daily or dalteparin 5,000 units daily) 1, 2
• OR warfarin with goal INR 2.0-3.0 (with initial LMWH overlap) 1, 2

Both LMWH and warfarin are safe during breastfeeding as neither is secreted in breast milk 1, 2.

Safety and Monitoring

• LMWH is strongly preferred over unfractionated heparin for both prophylaxis and treatment in pregnancy (Grade 1A recommendation) 1, 3, 2
• Routine anti-factor Xa monitoring is not recommended for standard prophylactic dosing 2
• LMWH does not cross the placenta and is safe for the fetus 6
• Maternal side effects are uncommon: mild localized allergic reactions occur in approximately 2% and increased bleeding in 2% (dose-dependent) 6
• Heparin-induced thrombocytopenia is very rare with LMWH 6

Common Pitfalls to Avoid

• Do not use prophylactic doses for acute DVT treatment—this is inadequate anticoagulation and risks treatment failure 3, 5
• Do not use warfarin during pregnancy—it crosses the placenta and causes embryopathy 3
• Do not use DOACs in pregnancy—there is insufficient safety data 1, 2
• Do not forget postpartum prophylaxis—the risk of VTE extends 6 weeks postpartum in women with prior VTE 1, 2
• Do not assume fixed dosing is adequate throughout pregnancy for therapeutic anticoagulation—85% of pregnant women on therapeutic LMWH require dose escalation to maintain therapeutic levels 5

Evidence Quality

These recommendations are based on Grade 2C evidence (weak recommendation, low-quality evidence) from the American College of Chest Physicians, reflecting the paucity of high-quality randomized trials in pregnant populations 1, 3. The dosing recommendations are extrapolated from non-pregnant populations and observational studies in pregnancy 1.