What is the most appropriate anticoagulation therapy for a 26-week pregnant woman with deep vein thrombosis (DVT), who has been on bedrest for two weeks and presents with pain and warmth in her right leg, tachycardia, mild hypertension, and normal body temperature?

Anticoagulation for DVT in Pregnancy

For this 26-week pregnant woman with confirmed DVT, initiate low-molecular-weight heparin (LMWH) immediately and continue throughout pregnancy and for at least 6 weeks postpartum, with a minimum total treatment duration of 3 months from diagnosis. 1, 2, 3

First-Line Therapy: LMWH

LMWH is the definitive first-line anticoagulant for acute DVT in pregnancy, strongly preferred over all other options. 1, 2, 3

• LMWH does not cross the placenta, ensuring fetal safety while providing superior maternal anticoagulation compared to unfractionated heparin 3, 4
• The American College of Chest Physicians gives LMWH a Grade 1B recommendation (strong recommendation, moderate-quality evidence) for both prevention and treatment of VTE in pregnancy 1, 2
• LMWH offers superior bioavailability, more predictable anticoagulant response, and significantly reduced risk of heparin-induced thrombocytopenia compared to unfractionated heparin 2, 3

Specific Management for This Patient

Given the 9-day symptom duration and confirmed external iliac vein occlusion, this patient requires therapeutic-dose LMWH initiated immediately. 1

• For acute iliofemoral DVT in a pregnant patient with moderate to severe symptoms, anticoagulation alone is the appropriate initial therapy 1
• The ACR Appropriateness Criteria (2020) specifically designates anticoagulation alone as "usually appropriate" for pregnant patients with acute iliofemoral DVT and moderate to severe symptoms (Variant 7) 1
• Catheter-directed thrombolysis and surgical thrombectomy should be avoided in pregnancy due to radiation exposure and procedural risks unless limb-threatening ischemia develops 1

Treatment Duration and Postpartum Management

Continue therapeutic anticoagulation throughout the remainder of pregnancy and for at least 6 weeks postpartum, ensuring a minimum total treatment duration of 3 months from diagnosis. 1, 2, 3

• The American College of Chest Physicians recommends anticoagulation for at least 6 weeks postpartum with a minimum total duration of 3 months (Grade 2C) 1, 2
• Meta-analysis data shows LMWH during pregnancy has a recurrent VTE rate of only 1.97% and major bleeding rate of 1.41% antepartum, demonstrating excellent safety and efficacy 5

Peripartum Anticoagulation Management

Plan scheduled delivery with discontinuation of LMWH at least 24 hours before anticipated delivery or neuraxial anesthesia. 2, 3, 6

• This 24-hour window allows adequate clearance to minimize bleeding risk during delivery while maintaining therapeutic anticoagulation until the last safe moment 2, 3
• After delivery, either continue LMWH or transition to warfarin, as both are safe during breastfeeding 1, 3
• Warfarin, unfractionated heparin, and LMWH are all compatible with breastfeeding (Grade 1A for warfarin/UFH, Grade 1B for LMWH) 1, 3

Critical Contraindications to Avoid

Never use warfarin during pregnancy, especially in the first trimester, due to teratogenicity and fetal bleeding risks. 1, 2, 3

• Warfarin causes embryopathy when used in the first trimester and increases fetal bleeding risk at delivery (Grade 1A contraindication) 1, 2, 3
• Direct oral anticoagulants (DOACs including dabigatran, rivaroxaban, apixaban) are absolutely contraindicated in pregnancy due to lack of safety data and potential fetal harm (Grade 1C) 1, 2

Monitoring Considerations

Routine anti-factor Xa monitoring is not recommended for pregnant women on therapeutic LMWH unless specific concerns about therapeutic levels exist. 1, 3

• The American Society of Hematology 2018 guidelines do not recommend routine anti-factor Xa monitoring to guide dose adjustment in pregnant women receiving therapeutic-dose LMWH 1
• Clinical monitoring for bleeding and thrombotic complications is sufficient in most cases 3, 4

Common Pitfalls

• Delaying anticoagulation initiation: Start LMWH immediately upon DVT diagnosis—pregnancy-associated VTE is a leading cause of maternal mortality 1, 2
• Inadequate treatment duration: Many clinicians stop anticoagulation too early; the minimum is 3 months total with at least 6 weeks postpartum 1, 2
• Using unfractionated heparin instead of LMWH: While UFH is acceptable, LMWH is strongly preferred due to superior efficacy and safety profile 1, 2, 3
• Continuing LMWH too close to delivery: Failure to discontinue LMWH 24 hours before delivery increases hemorrhagic complications and precludes neuraxial anesthesia 2, 3