What are the ACOG recommendations for venous thromboembolism prophylaxis in pregnant and postpartum women, including risk assessment, pharmacologic and mechanical methods, dosing, and duration?

ACOG Guidelines on Thromboprophylaxis in Pregnancy and Postpartum

All women undergoing cesarean delivery must receive mechanical prophylaxis with sequential compression devices (SCDs) starting before surgery and continuing until fully ambulatory, regardless of other risk factors. 1, 2

Universal Mechanical Prophylaxis

• Sequential compression devices are mandatory for every cesarean delivery, applied preoperatively and maintained throughout hospitalization until complete ambulation is achieved (GRADE 1C). 1, 2
• Pneumatic sequential compression devices are superior to static elastic stockings for preventing perioperative VTE in obstetric patients. 2
• This recommendation applies universally—even low-risk patients without additional VTE risk factors require mechanical prophylaxis. 2

Risk Stratification Framework

ACOG recommends systematic screening of all pregnant women for VTE risk factors but does not endorse a single specific risk stratification tool. 1 Instead, ACOG encourages hospitals to implement a protocol using available frameworks (ACCP, RCOG, or NPMS) while weighing benefits, harms, and cost-effectiveness. 1

Major Risk Factors (Any One Triggers Pharmacologic Prophylaxis)

• Prior personal history of deep vein thrombosis or pulmonary embolism 2, 3
• High-risk inherited thrombophilia: antithrombin deficiency, homozygous Factor V Leiden or prothrombin G20210A, compound heterozygosity for both 1, 2, 3
• Antiphospholipid antibody syndrome 2, 3
• Antepartum immobility ≥1 week 2
• Preeclampsia with fetal growth restriction 2

Minor Risk Factors (Two or More Trigger Pharmacologic Prophylaxis)

• Advanced maternal age (≥35 years, with ≥45 years carrying higher risk) 2
• Obesity (BMI ≥30; Class I obesity BMI 30-34.9 is a minor factor) 2
• Current smoking 2
• Family history of VTE 2
• Varicose veins 2

The ACCP framework suggests pharmacologic prophylaxis when absolute VTE risk exceeds 3%, which occurs with one major risk factor OR two or more minor risk factors. 1, 2

Pharmacologic Prophylaxis

Agent Selection

Low-molecular-weight heparin (enoxaparin) is the preferred agent for VTE prophylaxis during pregnancy and the postpartum period (GRADE 1C). 2, 3, 4

• Warfarin and direct oral anticoagulants (DOACs) should not be used for prophylaxis in the immediate postpartum period. 2
• Aspirin has no role in VTE prophylaxis after cesarean delivery. 2

Standard Dosing

• Enoxaparin 40 mg subcutaneously once daily for patients with standard risk profiles (one major or two minor risk factors). 2
• For patients with creatinine clearance <30 mL/min, substitute unfractionated heparin 5,000-10,000 units subcutaneously every 8-12 hours. 2

Obesity-Adjusted Dosing

For Class III obesity (BMI ≥40), use intermediate-dose enoxaparin 40 mg subcutaneously every 12 hours rather than standard once-daily dosing (GRADE 2C). 2 This is critical because standard dosing results in subtherapeutic anti-Xa levels in the majority of patients with BMI ≥40. 2

Timing of Initiation

• Standard prophylactic dosing (40 mg once daily) can be initiated 12 hours after neuraxial block or 4-6 hours after vaginal delivery. 2, 5
• Intermediate dosing (40 mg every 12 hours) must not be started before 24 hours after neuraxial block to minimize spinal hematoma risk. 2
• After cesarean delivery without neuraxial anesthesia, initiate 6-12 hours postoperatively when hemostasis is assured. 2, 5

Duration of Prophylaxis

• Mechanical prophylaxis continues until the patient is fully ambulatory. 1, 2
• Pharmacologic prophylaxis should be extended to 6 weeks postpartum when risk factors persist (GRADE 2C). 1, 2, 3
• For intermediate-risk patients (one major or two minor risk factors), a minimum of 10 days of pharmacologic prophylaxis is recommended. 2, 5

High-Risk Populations Requiring Extended Combined Prophylaxis

Women with prior VTE or any inherited thrombophilia (high-risk or low-risk) require both mechanical and pharmacologic prophylaxis for 6 weeks postpartum (GRADE 2C). 1, 2, 3

• This applies to all women with previous VTE, regardless of whether it was provoked or unprovoked. 1, 2, 3
• Women with antiphospholipid antibody syndrome also require 6 weeks of combined prophylaxis. 2, 3
• For women receiving adjusted-dose LMWH therapy antepartum, discontinue at least 24 hours before planned cesarean section to allow safe neuraxial anesthesia, then resume therapeutic anticoagulation postoperatively. 2

Low-Risk Patients

For women undergoing cesarean delivery without additional risk factors, early mobilization plus mechanical prophylaxis (SCDs) is sufficient—pharmacologic prophylaxis is not recommended (GRADE 1B). 2 Adding anticoagulation in this population increases bleeding risk without meaningful VTE reduction. 2

Common Pitfalls to Avoid

• Do not use standard-dose enoxaparin (40 mg once daily) in Class III obesity—this is inadequate and results in subtherapeutic levels. 2
• Do not initiate intermediate-dose enoxaparin before 24 hours post-neuraxial block—this significantly increases spinal hematoma risk. 2
• Do not rely on early ambulation alone when two or more minor risk factors are present—this is appropriate only for patients with no identified VTE risk factors. 2
• Do not use DOACs or warfarin for postpartum prophylaxis—insufficient safety data exist for these agents in the immediate postpartum period. 2

Institutional Implementation

The Society for Maternal-Fetal Medicine recommends that each institution develop a standardized patient-safety bundle with a VTE prophylaxis protocol specific to cesarean delivery (Best Practice). 1, 2 Standardized order sets reduce practice variation and improve compliance with evidence-based prophylaxis. 2

Key Bundle Components

• Preoperative SCD application for all cesarean deliveries 2
• Risk factor screening using a validated tool (ACCP, RCOG, or modified Caprini) 1
• Weight-based LMWH dosing protocols 5
• Renal function screening before enoxaparin initiation 2
• Clear documentation of neuraxial anesthesia timing to guide LMWH initiation 2