Anticoagulation during pregnancy

Managing anticoagulation in pregnancy: risk categories, treatment timing, and duration. From EHA 2025 congress, what clinicians need to know.

Pregnancy, a prothrombotic condition that needs to be treated? Who, how and for how long?

Pregnancy induces a well-recognized prothrombotic state due to profound physiological changes in the coagulation system. The management of anticoagulation during pregnancy remains a complex clinical challenge, requiring careful balancing of maternal and fetal risks. In his presentation at EHA 2025, “Anticoagulation during pregnancy: who, when and for how long,” Dr. Marc Blondom (Division of Angiology and Haemostasis, Geneva University Hospitals) provided an evidence-based overview of current strategies and practical recommendations for clinicians.

Who to treat: identifying risk categories

Dr. Blondom opened his presentation by emphasizing the importance of risk stratification. Not all pregnant women require anticoagulation. Appropriate selection hinges on a careful assessment of thrombotic risk factors.

Key groups to consider for prophylactic or therapeutic anticoagulation include:

• women with a history of venous thromboembolism (VTE), particularly in unprovoked or hormonally related cases;
• women with thrombophilia, especially antithrombin deficiency, homozygous factor V Leiden, prothrombin gene mutations, or antiphospholipid syndrome;
• women with mechanical heart valves (high-risk subgroup requiring therapeutic anticoagulation);
• women with severe inherited thrombophilia, with or without a personal or family history of thrombosis.

It is important to note that pregnancy-related risk factors, such as immobilisation, caesarean section, obesity or multiple pregnancy, can alter the overall risk and should influence treatment decisions.

Dr. Blondom stressed that individual risk assessment remains paramount: blanket anticoagulation for all thrombophilic women is not warranted, and overtreatment can introduce unnecessary bleeding risk.

When to start anticoagulation

Optimal timing for initiating anticoagulation depends on baseline risk and prior clinical history. For high-risk patients (e.g., with a history of VTE), anticoagulant therapy is usually started before conception or as soon as pregnancy is confirmed. For patients identified during pregnancy (e.g., with a diagnosis of a new episode of VTE), treatment should be started immediately after diagnosis.

In women with intermediate risk (e.g., heterozygous thrombophilia without prior thrombosis), prophylactic anticoagulation may be considered starting from the second trimester, when the hypercoagulable state intensifies.

Dr. Blondom also discussed perioperative and peripartum management, highlighting the importance of close coordination between obstetricians and hematologists. Ideally, delivery should be planned to allow for temporary cessation of anticoagulation, thereby minimizing bleeding risk during labor. In emergency situations, the use of reversal agents or the administration of regional anesthesia requires careful timing in relation to the patient’s anticoagulation status.

For how long to continue treatment?

Duration of anticoagulation must encompass both pregnancy and the high-risk postpartum period, when thrombotic risk peaks. Dr. Blondom highlighted that:

• for therapeutic anticoagulation, treatment generally continues for the entire pregnancy and 6 weeks postpartum;
• for prophylactic anticoagulation, especially in women with minor risk factors, clinicians may consider adjusting duration based on risk assessment at delivery. However, a minimum of 6 weeks postpartum remains recommended for most women receiving antenatal anticoagulation.

He also underlined that many VTE events occur postpartum (thus, adequate postpartum coverage is critical). Early mobilization, compression therapy, and thromboprophylaxis are key components of comprehensive care.

Choice of anticoagulant

Although not the primary focus of this session, Dr. Blondom briefly reviewed drug selection.

1. Low Molecular Weight Heparin (LMWH) remains the mainstay of therapy, given its safety profile and lack of placental transfer.
2. Vitamin K Antagonists (VKA) are generally avoided during pregnancy but may be necessary for women with mechanical valves.
3. Direct Oral Anticoagulants (DOACs) are not routinely recommended due to insufficient safety data in pregnancy.

Take-home messages

In his concluding remarks, Dr. Blondom reinforced key principles for clinical practice:

• anticoagulation during pregnancy must be individualized, guided by personal risk factors, clinical history, and ongoing risk assessments;
• multidisciplinary collaboration is essential to optimize outcomes and manage complex cases;
• adequate postpartum thromboprophylaxis is critical, as risk persists beyond delivery.

As research continues to evolve, clinicians must remain attentive to updated guidelines and emerging data on the safety of newer agents. For now, LMWH-based regimens, tailored to patient risk profiles, remain the standard of care for managing anticoagulation during pregnancy.