Low Molecular Weight Heparin for DVT Prophylaxis in Pregnancy
Low molecular weight heparin (LMWH) is the strongly recommended anticoagulant for DVT prophylaxis in pregnant women, administered subcutaneously once or twice daily at prophylactic or intermediate doses depending on risk stratification, and should be continued for at least 6 weeks postpartum. 1
Choice of Anticoagulant
LMWH is strongly preferred over unfractionated heparin (UFH) for both prevention and treatment of VTE in pregnancy (Grade 1B), offering superior bioavailability, more predictable pharmacokinetics, and significantly lower risk of heparin-induced thrombocytopenia and osteoporosis 1, 2, 3
LMWH does not cross the placental barrier and poses no teratogenic risk to the fetus, making it the safest option for both mother and baby 4
Warfarin must be avoided entirely during the first trimester due to teratogenicity and throughout pregnancy due to fetal bleeding risks (Grade 1A) 1, 2
Direct oral anticoagulants (DOACs including dabigatran, rivaroxaban, apixaban) are absolutely contraindicated in pregnancy (Grade 1C) 1, 2
Risk-Stratified Dosing Regimens
Low-Risk Women (Group I):
- Prophylactic-dose LMWH: 50-100 IU/kg body weight once daily 5
- Initiate when additional risk factors occur (prolonged bed rest, operative delivery, preeclampsia) 5, 6
- Continue for at least 14 days postpartum or 6 weeks if higher risk features develop 5
Moderate to High-Risk Women (Group II):
- Women with prior VTE, especially if unprovoked or hormone-associated, require antepartum prophylaxis 1, 7
- Prophylactic or intermediate-dose LMWH: 50-100 IU/kg body weight once daily throughout pregnancy 7, 5
- Continue for 6 weeks postpartum with minimum total duration of 3 months from any acute event 1, 2
Very High-Risk Women (Group III):
- Women requiring long-term anticoagulation, homozygous factor V Leiden or prothrombin 20210A mutation with positive family history 7
- Intermediate to therapeutic-dose LMWH: 100-200 IU/kg body weight once daily throughout pregnancy 5
- Continue for 6 weeks postpartum 7
Specific LMWH Options and Dosing Frequency
Either once-daily or twice-daily dosing regimens are acceptable for therapeutic anticoagulation, though once-daily dosing improves compliance 1, 8
Common agents include enoxaparin and dalteparin, both demonstrating safety and efficacy in pregnancy 3, 8
Routine anti-factor Xa monitoring is not recommended for dose adjustment in most cases (Grade 2C), though levels can be checked 4-6 hours after morning dose if needed (target 0.7-1.2 units/mL for therapeutic dosing) 1, 4
Peripartum Management
Discontinue LMWH at least 24 hours before planned induction of labor, cesarean section, or neuraxial anesthesia (Grade 1B) to minimize hemorrhagic complications 2, 4
Resume anticoagulation postpartum once hemostasis is secured, typically 6-12 hours after vaginal delivery or 12-24 hours after cesarean section 9
Postpartum Anticoagulation
All women receiving antepartum prophylaxis require postpartum anticoagulation for at least 6 weeks with either prophylactic/intermediate-dose LMWH or warfarin (INR 2.0-3.0) 7, 4
For women treated for acute VTE during pregnancy, continue anticoagulation for minimum total duration of 3 months from diagnosis (Grade 2C) 1, 2
LMWH, UFH, and warfarin are all safe during breastfeeding and can be continued without interruption (Grade 1A for warfarin/UFH, Grade 1B for LMWH) 1, 2
Special Populations Requiring Prophylaxis
Women with antiphospholipid antibody syndrome and recurrent pregnancy loss:
Women with prior VTE associated with resolved non-hormonal provoking factor:
- Conditional recommendation against routine antepartum prophylaxis, but strongly recommend postpartum prophylaxis for 6 weeks 1
Populations NOT Requiring Prophylaxis
Women with inherited thrombophilia and history of pregnancy complications without prior VTE should not receive antithrombotic prophylaxis (Grade 2C) 1, 4
Women with two or more miscarriages but without antiphospholipid antibodies or thrombophilia should not receive antithrombotic prophylaxis (Grade 1B) 1, 4
Common Pitfalls to Avoid
Failure to distinguish between thrombophilia types: Homozygous factor V Leiden and prothrombin 20210A mutations carry substantially higher risk than heterozygous states and require more aggressive prophylaxis 7
Inadequate postpartum duration: The postpartum period carries equal or higher thrombotic risk than antepartum; 6 weeks of postpartum anticoagulation is mandatory, not optional 7, 4
Using warfarin in first trimester: This causes embryopathy and must be avoided; switch to LMWH before conception or immediately upon pregnancy confirmation 1, 2
Continuing LMWH too close to delivery: Failure to discontinue LMWH 24 hours before neuraxial anesthesia risks epidural hematoma 2, 4