What is the recommended pharmacologic (low‑molecular‑weight heparin) and mechanical prophylaxis for deep‑vein thrombosis in pregnant women, especially those with high‑risk factors?

DVT Prophylaxis During Pregnancy

Pregnant women require risk-stratified thromboprophylaxis using low-molecular-weight heparin (LMWH) as the preferred agent, with specific dosing and duration determined by individual VTE risk factors, prior thrombotic history, and thrombophilia status. 1

Agent Selection

• LMWH (enoxaparin or dalteparin) is the anticoagulant of choice for both prophylaxis and treatment of VTE during pregnancy, superior to unfractionated heparin in efficacy, safety, and convenience (Grade 1A). 1
• LMWH does not cross the placental barrier, eliminating fetal anticoagulation risk. 2, 3
• Vitamin K antagonists (warfarin) are contraindicated during pregnancy due to embryopathy and fetal bleeding risk (Grade 1A). 1, 3
• Direct oral anticoagulants (DOACs) should be avoided due to insufficient safety data (Grade 1C). 1

Risk Stratification for Antepartum Prophylaxis

High-Risk Patients Requiring Antepartum LMWH

• Women with prior unprovoked VTE should receive prophylactic- or intermediate-dose LMWH throughout pregnancy (Grade 2C). 1, 4
• Women with pregnancy- or estrogen-related prior VTE require antepartum prophylaxis with prophylactic- or intermediate-dose LMWH (Grade 2C). 1, 4
• Women with multiple prior unprovoked VTE episodes not on long-term anticoagulation need antepartum prophylactic- or intermediate-dose LMWH (Grade 2C). 1, 4
• Women on long-term vitamin K antagonists should receive adjusted-dose LMWH (75% of therapeutic dose) throughout pregnancy, then resume long-term anticoagulation postpartum (Grade 2C). 1, 4

Thrombophilia-Specific Indications

• Homozygous factor V Leiden or prothrombin G20210A mutation with positive family history warrants antepartum prophylaxis with prophylactic-dose LMWH (Grade 2C). 1
• Antithrombin deficiency with family history of VTE requires both antepartum and postpartum prophylaxis. 4
• Combined thrombophilias (compound heterozygosity) mandate antepartum and postpartum prophylaxis regardless of family history. 4

Low-Risk Patients NOT Requiring Antepartum Prophylaxis

• Women with single prior VTE associated with a transient risk factor (not pregnancy or estrogen-related, such as surgery or trauma) should receive clinical vigilance only during pregnancy, not prophylactic LMWH (Grade 2C). 1, 4

Dosing Regimens

Prophylactic Dosing (Standard Risk)

• Enoxaparin 40 mg subcutaneously once daily throughout pregnancy. 1, 4
• Dalteparin 5,000 units subcutaneously once daily throughout pregnancy. 1, 4

Intermediate Dosing (Moderate-High Risk)

• Enoxaparin 40 mg subcutaneously every 12 hours, or dose-adjusted to achieve anti-Xa levels 0.2–0.6 U/mL. 1, 4

Adjusted-Dose Therapeutic LMWH (Acute VTE or Very High Risk)

• Enoxaparin 1 mg/kg subcutaneously every 12 hours, or 1.5 mg/kg once daily. 1
• For women on long-term anticoagulation, use 75% of therapeutic dose throughout pregnancy (Grade 2C). 1, 4

Monitoring

• Routine anti-Xa monitoring is NOT recommended for prophylactic dosing in most pregnant women. 4, 5
• Anti-Xa monitoring may be considered in women with extreme body weight, renal insufficiency, or mechanical heart valves, though evidence does not demonstrate improved outcomes. 5
• Platelet count monitoring should begin on day 4 of therapy to screen for heparin-induced thrombocytopenia. 6

Peripartum Management

• Discontinue LMWH at least 24 hours before planned induction of labor, cesarean section, or neuraxial anesthesia to minimize bleeding risk (Grade 1B). 1, 4
• For spontaneous labor, withhold LMWH when contractions begin. 1
• Resume therapeutic anticoagulation postoperatively once hemostasis is assured, typically 12–24 hours after delivery. 1

Postpartum Prophylaxis (Universal for Prior VTE)

• All pregnant women with any prior VTE history should receive 6 weeks of postpartum prophylaxis with prophylactic- or intermediate-dose LMWH, or warfarin (INR 2.0–3.0), regardless of antepartum management (Grade 2B). 1, 4
• This recommendation applies even to women with low-risk prior VTE who did not receive antepartum prophylaxis. 1, 4

Cesarean Section-Specific Prophylaxis

Standard-Risk Cesarean (No Additional Risk Factors)

• Early mobilization alone is sufficient; pharmacologic prophylaxis is not recommended (Grade 1B). 1, 6

Increased-Risk Cesarean (≥1 Major or ≥2 Minor Risk Factors)

• Prophylactic LMWH (enoxaparin 40 mg once daily) or mechanical prophylaxis (sequential compression devices or elastic stockings) while hospitalized (Grade 2B). 1, 6
• Mechanical prophylaxis is preferred when anticoagulation is contraindicated due to bleeding risk. 1

Very High-Risk Cesarean (Multiple Persistent Risk Factors)

• Combine prophylactic LMWH with elastic stockings and/or intermittent pneumatic compression rather than LMWH alone (Grade 2C). 1, 6
• Extended prophylaxis up to 6 weeks after discharge is suggested when risk factors persist (Grade 2C). 1, 6

Treatment of Acute VTE During Pregnancy

• Adjusted-dose subcutaneous LMWH is preferred over adjusted-dose unfractionated heparin for acute VTE treatment (Grade 1B). 1
• LMWH is preferred over vitamin K antagonists for antenatal treatment (Grade 1A). 1
• Anticoagulation should continue for at least 6 weeks postpartum, with a minimum total duration of 3 months (Grade 2C). 1

Special Populations

Severe Ovarian Hyperstimulation Syndrome

• Women who develop severe ovarian hyperstimulation syndrome should receive prophylactic LMWH for 3 months post-resolution (Grade 2C). 1, 4

Renal Impairment

• In patients with creatinine clearance <30 mL/min, unfractionated heparin (5,000–10,000 units subcutaneously every 8–12 hours) should replace LMWH. 6

Common Pitfalls to Avoid

• Do not withhold postpartum prophylaxis in women with prior VTE, even if they had low-risk transient provoked events and did not receive antepartum prophylaxis—6 weeks of postpartum LMWH is still indicated. 1, 4
• Do not continue LMWH up to the time of delivery—this significantly increases bleeding and epidural hematoma risk; stop at least 24 hours before planned delivery. 1, 4
• Do not use prophylactic anticoagulation in low-risk cesarean patients without additional risk factors—the number needed to harm exceeds the number needed to treat. 6
• Do not assume all thrombophilias require antepartum prophylaxis—only high-risk thrombophilias (homozygous mutations, compound heterozygosity, antithrombin deficiency) or those with prior VTE warrant antepartum LMWH. 1, 4
• Do not use fixed-dose prophylaxis in morbidly obese patients (BMI ≥40)—intermediate dosing (enoxaparin 40 mg every 12 hours) is required. 6