American Society of Hematology Guidelines for Thrombophilia in Pregnancy
The ASH 2018 guidelines recommend a risk-stratified approach to thrombophilia management in pregnancy, with most women requiring only clinical surveillance antepartum but selective use of postpartum prophylaxis based on thrombophilia type and family history of VTE. 1
Key Principles
The management strategy depends on three critical factors: the specific type of thrombophilia, presence or absence of a first-degree family history of VTE (especially before age 50), and whether the woman has had a prior VTE herself. 1
Heterozygous Factor V Leiden or Prothrombin Gene Mutation
Antepartum Management
- Clinical surveillance alone is recommended—no prophylactic anticoagulation—regardless of family history of VTE. 1, 2
- This is a conditional recommendation based on very low certainty evidence, reflecting the low absolute risk of antepartum VTE (<1%) in this population. 1
Postpartum Management
- Without family history of VTE: Suggest against routine postpartum prophylaxis (conditional recommendation). 1
- With family history of VTE: Still suggest against postpartum prophylaxis, though the postpartum VTE risk is 0.62% for factor V Leiden and 0.95% for prothrombin mutation. 1
- Exception: Consider prophylactic or intermediate-dose LMWH for 6 weeks postpartum if there are ≥2 additional risk factors (obesity BMI ≥30, smoking, emergency cesarean, prolonged labor >24 hours, postpartum hemorrhage >1L). 1
Protein C or Protein S Deficiency
Antepartum Management
- Without family history: Clinical surveillance only (conditional recommendation). 1
- With family history: The panel could not make a firm evidence-based recommendation, but generally favored clinical surveillance over prophylaxis. 1
Postpartum Management
- Without family history: Suggest against routine prophylaxis. 1
- With family history: Suggest postpartum prophylactic or intermediate-dose LMWH for 6 weeks (conditional recommendation, very low certainty evidence). 1
- The postpartum VTE risk with family history is 1.76% for protein S deficiency and 1.06% for protein C deficiency. 1
Antithrombin Deficiency
Antepartum Management
- Without family history: The panel could not make a firm recommendation but generally favored clinical surveillance. 1
- With family history: The panel could not make a firm evidence-based recommendation, though some members favored prophylaxis given higher risk. 1
Postpartum Management
- With family history: Strong recommendation for postpartum prophylaxis (moderate certainty evidence)—this is the only strong recommendation in the thrombophilia guidelines. 1
- The postpartum VTE risk with family history is 4.83%, substantially higher than other thrombophilias. 1
- Without family history: Suggest against routine prophylaxis. 1
Homozygous Factor V Leiden or Prothrombin Gene Mutation
Antepartum Management
- Homozygous factor V Leiden: Suggest antepartum prophylaxis regardless of family history (conditional recommendation). 1
- Homozygous prothrombin mutation without family history: Suggest against antepartum prophylaxis. 1
- Homozygous prothrombin mutation with family history: No evidence-based recommendation possible, but panel members generally favored prophylaxis. 1
Postpartum Management
- Both mutations, regardless of family history: Suggest postpartum prophylactic or intermediate-dose LMWH or warfarin (INR 2.0-3.0) for 6 weeks (conditional recommendation). 1
- The postpartum VTE risk is 5.87% for homozygous factor V Leiden. 1
Compound Heterozygosity (e.g., Factor V Leiden + Prothrombin Mutation)
Antepartum Management
- Regardless of family history: Suggest antepartum prophylaxis (conditional recommendation, very low certainty evidence). 1
Postpartum Management
- Without family history: Suggest clinical surveillance only. 1
- With family history: Suggest postpartum prophylactic or intermediate-dose LMWH or warfarin (INR 2.0-3.0) for 6 weeks (conditional recommendation). 1
- The postpartum VTE risk with family history is approximately 3.99%. 1
Anticoagulation Regimens When Prophylaxis Is Indicated
Preferred Agent
- LMWH is strongly preferred over unfractionated heparin due to more predictable therapeutic levels, superior efficacy, lower risk of heparin-induced thrombocytopenia, and reduced osteoporosis risk. 3, 4
Dosing Options
- Prophylactic-dose LMWH: Enoxaparin 40 mg subcutaneously once daily. 1
- Intermediate-dose LMWH: Enoxaparin 40 mg subcutaneously twice daily or weight-adjusted dosing. 1
- Postpartum warfarin: Target INR 2.0-3.0 is an acceptable alternative to LMWH for 6 weeks postpartum. 1
Monitoring
- Routine anti-factor Xa monitoring is not required unless there are specific concerns (extreme body weight, renal impairment, uncertain therapeutic effect). 3, 4
Medications to Avoid in Pregnancy
- Vitamin K antagonists (warfarin) are contraindicated due to embryopathy risk and potential fetal bleeding. 1, 3
- Direct oral anticoagulants (dabigatran, apixaban, edoxaban, rivaroxaban) must not be used due to placental transfer and insufficient safety data. 1, 3
- Fondaparinux should be avoided as it crosses the placenta with inadequate safety evidence. 3
Peripartum Management
- Discontinue LMWH 24 hours before scheduled delivery (induction or cesarean) to minimize bleeding risk. 3, 4
- Resume anticoagulation 8-12 hours after vaginal delivery or 12-24 hours after cesarean section if bleeding is controlled. 3, 4
- For neuraxial anesthesia: LMWH must be stopped at least 24 hours prior to epidural or spinal placement. 3
Breastfeeding
- LMWH, unfractionated heparin, and warfarin are all safe during breastfeeding and do not require cessation of nursing. 3
Common Pitfalls to Avoid
- Do not use prophylactic anticoagulation for heterozygous factor V Leiden or prothrombin mutation without additional risk factors—the absolute VTE risk is too low to justify routine prophylaxis. 1, 2
- Do not overlook antithrombin deficiency with family history—this is the only scenario warranting a strong recommendation for postpartum prophylaxis. 1
- Do not continue prophylaxis beyond 6 weeks postpartum unless there are other indications, as pregnancy-associated hypercoagulability resolves by this time. 1, 3
- Do not perform thrombophilia testing during acute thrombosis or the initial 3-month anticoagulation period, as results may be unreliable. 5
Testing Recommendations
The ASH 2023 guidelines on thrombophilia testing recommend against routine screening of the general population or asymptomatic pregnant women. 6 Testing may be considered in highly selective scenarios:
- Pregnant women with a family history of high-risk thrombophilia types (antithrombin, protein C, protein S deficiency, or homozygous mutations) when results would change management decisions. 6
- Women with prior VTE associated with hormonal risk factors where testing might influence duration of anticoagulation. 6
- Testing should only be performed when results will directly impact clinical decisions and potential benefits outweigh risks. 6, 5