Heparin dosing during pregnancy

Indication	Type of heparin	Dosing information
VTE prevention	LMW heparin	Low dose (also called prophylactic dose): Enoxaparin: Weight <100 kg: 40 mg SUBQ once daily Weight ≥100 kg: 60 mg SUBQ once daily or Dalteparin: Weight <100 kg: 5000 units SUBQ once daily Weight ≥100 kg: 7500 units SUBQ once daily
	LMW heparin	Intermediate dose^*: Enoxaparin 40 mg SUBQ once daily, increase as pregnancy progresses and weight increases to 1 mg/kg once daily or Dalteparin 5000 units SUBQ once daily, increase as pregnancy progresses and weight increases to 100 units/kg once daily
	UFH	According to trimester^¶: First trimester: 5000 to 7500 units SUBQ every 12 hours Second trimester: 7500 to 10,000 units SUBQ every 12 hours Third trimester: 10,000 units SUBQ every 12 hours
VTE treatment (therapeutic dose)	LMW heparin	Enoxaparin 1 mg/kg SUBQ every 12 hours or Dalteparin 100 units/kg SUBQ every 12 hours
VTE treatment (therapeutic dose)	UFH	Can be given as a continuous IV infusion or SUBQ dose every 12 hours. Titrated to keep the aPTT in the therapeutic range.

This table applies to VTE in pregnant individuals, with the exception of individuals with a prosthetic heart valve, which is discussed separately in UpToDate.

Dose level – Prevention typically uses low or intermediate dose, but therapeutic dose may be used for prevention in selected cases (eg, individuals with recurrent unprovoked thrombotic events [with or without hereditary thrombophilia or antiphospholipid antibody syndrome] who are receiving long-term anticoagulation with warfarin or a direct oral anticoagulant such as rivaroxaban 20 mg daily or apixaban 5 mg twice daily).
Choice of agent – LMW heparin is recommended for most patients. UFH is used when there may be a need for rapid discontinuation, such as for delivery or perioperatively or in individuals with severely reduced kidney function (eg, CrCl <30 mL/min). Only one heparin product is given at any point in time. Confirm the absence of preservatives (eg, benzyl alcohol) in the heparin product chosen.

Refer to UpToDate for anticoagulation indications, choice of dose level, duration of pharmacologic therapy, and timing of switches between LMW heparin and UFH.

ACCP: American College of Chest Physicians; ACOG: American College of Obstetricians and Gynecologists; aPTT: activated partial thromboplastin time; CrCl: creatinine clearance; IV: intravenous; LMW: low molecular weight; SUBQ: subcutaneously; UFH: unfractionated heparin; VTE: venous thromboembolism.

* Our "intermediate" dose level differs from that used in society guidelines (eg, ACCP, ACOG). Some clinicians prefer to use a different "intermediate" dose level such as enoxaparin 40 mg SUBQ every 12 hours; however, this entails a significant increase in the number of injections over the course of the pregnancy.

¶ Some clinicians use 5000 units SUBQ every 12 hours throughout the pregnancy; however, this dose may be insufficient in some patients.

Courtesy of Kenneth A Bauer, MD; updated with data from:

Bistervels IM, Buchmüller A, Wiegers HMG, et al. Intermediate-dose versus low-dose low-molecular-weight heparin in pregnant and post-partum women with a history of venous thromboembolism (Highlow study): An open-label, multicentre, randomised, controlled trial. Lancet 2022; 400:1777.

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Heparin dosing during pregnancy