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Anticoagulant Therapy In Pregnancy

Editor: Suzanne M. Jenkins Updated: 1/10/2024 2:53:27 AM

Summary / Explanation

Pregnancy is a complex physiologic state that presents unique challenges, particularly when managing medical conditions that require anticoagulant therapy. Anticoagulant therapy plays a crucial role in preventing and managing thromboembolic events, which can be particularly challenging during pregnancy due to the hypercoagulable state that naturally occurs. Pregnant women are at an increased risk of venous thromboembolism (VTE) due to hormonal changes, increased blood volume, and changes in blood flow. The preferred anticoagulants for treating and preventing VTE in most pregnant patients include low molecular weight heparins (LMWH) and unfractionated heparin (UFH). Vitamin K antagonists (eg, warfarin), on the other hand, are known teratogens and, therefore, relatively contraindicated except in patients at extremely high risk for VTE (eg, those with mechanical heart valves). For these extremely high-risk patients, there is no clearly preferred anticoagulant, and the agent chosen must be individualized through a shared decision-making process between the patient and the healthcare team.[1]

The delicate balance between preventing thromboembolic events in the mother and ensuring the safety of the developing fetus makes anticoagulant therapy in pregnancy a topic of great importance. This article explores the various aspects of anticoagulant therapy during pregnancy, focusing on special considerations that healthcare professionals must consider.[2]

Anticoagulant Recommendations During Pregnancy

Selecting the appropriate anticoagulant during pregnancy involves careful consideration of both maternal and fetal factors. The choice must strike a balance between effectively preventing thromboembolic events in the mother and minimizing potential risks to the developing fetus. Several factors influence the decision-making process, and clinicians must tailor their choices based on each pregnant individual's unique characteristics and medical history.[3][4] The American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine have both published guidelines to help inform this choice.[4][1]

Low-Molecular-Weight Heparin

  • Advantages
    • LMWH (eg, enoxaparin or dalteparin) is typically the preferred choice for treatment and prophylaxis of VTE during pregnancy due to their efficacy, predictable pharmacokinetics, and safety profiles.
    • These agents do not cross the placenta in significant quantities, reducing the risk of adverse effects on fetal development.
    • LMWHs are available in pre-filled syringes, offering convenient subcutaneous administration without the need for frequent laboratory monitoring.[5][6]
  • Considerations
    • Therapeutic dosing (ie, for treatment of a current VTE) is weight-based during pregnancy.
    • Dosing adjustments should be made as recommended throughout gestation, especially in cases of obesity or extreme body weight.

Unfractionated Heparin

  • Advantages
    • UFH is a suitable alternative when LMWH is contraindicated or when more immediate reversibility is required.[7]
    • Unlike LMWH, UFH has a shorter half-life, facilitating quicker discontinuation in the event of urgent interventions or impending labor.
  • Considerations
    • UFH requires frequent monitoring of activated partial thromboplastin time (aPTT) to maintain therapeutic drug levels.
    • Dosing adjustments may be necessary as indicated by aPTT target.

Relative Contraindications

  • Warfarin
    • Warfarin crosses the placenta and has been associated with an increased risk of embryopathy, particularly when used during the first trimester.[8]
    • Due to its potential teratogenic effects, warfarin is generally avoided in pregnancy, especially during organogenesis.
    • Warfarin is generally contraindicated during pregnancy, except in cases where the benefits outweigh the risks, such as in patients with mechanical heart valves.[9][10] 
    • In patients with mechanical heart valves, warfarin is the preferred agent in nonpregnant individuals because its use leads to the lowest risk of valve thrombosis. Clinicians and patients must weigh the risk of valve thrombosis against the risk of congenital anomalies and make an individualized anticoagulation plan. Some patients may choose an LMWH in the first trimester, switching back to warfarin for the remainder of pregnancy.[1]
  • Direct oral anticoagulants 
    • Limited data are available on direct oral anticoagulants (DOACs) safety during pregnancy, and therefore generally not recommended.[11]
    • Placental transfer and potential effects on fetal development vary among different DOACs.
    • DOACs also should not be used during breastfeeding due to increased reproductive risks in animal studies and insufficient human safety and efficacy data.[12][13]

Peripartum Anticoagulant Therapy

Anticoagulation can increase the risk of epidural or spinal hematoma with neuraxial anesthesia. Therefore, patients receiving prophylactic LMWH during pregnancy are advised to discontinue anticoagulation at least 12 hours before a scheduled induction of labor or cesarean delivery. For pregnant women on adjusted-dose LMWH therapy with a planned delivery, LMWH discontinuation at least 24 hours before the scheduled induction of labor, cesarean section, or the anticipated time of neuraxial anesthesia is recommended, instead of maintaining LMWH up until the moment of delivery. In anticipation of delivery, women on anticoagulation therapy may be switched from a LMWH to UFH, which has a shorter half-life based on the institution's protocol. For patients on prophylactic LMWH during pregnancy, clinicians should wait at least 12 hours after neuraxial blockade and at least 4 hours after catheter removal to restart LMWH prophylaxis. For patients on intermediate or adjusted-dose LMWH, consider waiting at least 24 hours after neuraxial blockade and at least 4 hours after catheter removal to restart LMWH anticoagulation.[14]

Special Considerations for Anticoagulation Therapy in Pregnancy

  • Dosing adjustments: Pregnancy induces physiologic changes, including an increase in blood volume and changes in renal function. These alterations can impact the pharmacokinetics of anticoagulant drugs. Therefore, careful dosing adjustments are crucial to maintain therapeutic levels while minimizing the risk of bleeding.[15] Adjusted-dose (ie, therapeutic) LMWH regimens are weight-based, so dosing may require adjustments as a patient's weight naturally increases throughout pregnancy. 
  • Monitoring and laboratory tests: Regular monitoring with laboratory testing is sometimes needed to ensure efficacy and safety. Patients on UFH should be monitored to maintain an aPTT in the therapeutic range of 1.5 to 2.5 times the control 6 hours after the injection. Anticoagulation with LMWH can be monitored by following anti-factor Xa levels. However, the need to monitor these patients remains uncertain. For those on weight-based therapeutic doses, studies in which anti-factor Xa levels have been monitored with a goal of 0.6 to 1.0 units/mL, show that few patients will require dosing adjustments beyond those they would already receive as their weight naturally increases during pregnancy. The decision to monitor patients on therapeutic LMWH should, therefore, be based on institutional protocols and clinical judgment. Additionally, optimal anti-factor Xa levels have not been determined for patients receiving prophylactic LMWH, so patients on prophylactic doses rarely require regular monitoring. Finally, close attention should be given to routine laboratory tests, including platelet counts, to detect any signs of adverse effects of the anticoagulants (eg, heparin-induced thrombocytopenia).[16][17]
  • Fetal risk: While LMWH and UFH are considered safer options than vitamin K antagonists, a potential risk of adverse fetal outcomes (eg, bleeding at the uteroplacental junction) still exists. Clinicians must weigh the benefits of anticoagulation for the mother against potential risks to the fetus. Communication with the patient about these considerations is crucial for informed decision-making.
  • Timing of anticoagulant initiation and discontinuation: Initiating anticoagulant therapy early in pregnancy may be necessary for women with a history of thromboembolism or certain high-risk conditions (eg, thrombophilia and some cardiovascular disease). However, the timing of initiation and discontinuation must be carefully planned to minimize bleeding risks during labor and delivery.
  • Neonatal monitoring: Neonates born to mothers receiving anticoagulant therapy may be at an increased risk of bleeding complications. Pediatric clinicians should be informed that close monitoring for bleeding tendencies is essential during the neonatal period.[18]
  • Patient education and compliance: Patient education is paramount. Women on anticoagulant therapy during pregnancy must be well-informed about the importance of medication compliance, signs of bleeding or thrombosis, and the necessity of close follow-up with clinicians.
  • Individualized decision-making: The choice of anticoagulant should be individualized based on the woman's medical history, anticoagulation indication, and overall health. Consultation with a multidisciplinary team, including obstetricians, hematologists, and maternal-fetal medicine specialists, is crucial in making informed decisions.
  • Patient preferences and adherence: Involving the pregnant individual in decision-making is essential. Understanding patient preferences, lifestyle, and the ability to comply with the prescribed regimen enhances medication adherence.


Anticoagulant therapy in pregnancy requires a delicate balance between preventing thromboembolic events in the mother and ensuring the safety of the developing fetus. Special considerations, including dosing adjustments, monitoring, and careful evaluation of fetal risks, are essential components of managing anticoagulant therapy during pregnancy. Through a collaborative effort between clinicians and pregnant individuals, optimal outcomes can be achieved, safeguarding the well-being of both the mother and the unborn child. The benefits of preventing thromboembolic events must be carefully weighed against potential risks to the fetus. Clinicians should engage in open communication with pregnant individuals, empowering them to participate in decisions about their anticoagulant therapy actively, and fostering a collaborative approach to maternal and fetal health. In conclusion, the selection of anticoagulant therapy during pregnancy requires a thoughtful and individualized approach.[19]

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