Adjusting the anticoagulation regimen
CASE 2 Pregnant woman with prior VTE
A 36-year-old woman (G1P0) with prior VTE is taking enoxaparin 40 mg daily. She asks, does she need any blood work for her anticoagulation?
What would you test for?
Increased renal clearance of LMWH and increased volume of distribution during pregnancy has led to the consideration of monitoring anti-Xa levels. There are no published standards or recommendations for dose adjustment. At this time, anti-Xa level monitoring antepartum is not recommended, but it may be considered when a patient is at the extremes of weight. With a weight-based strategy in the postpartum period, monitoring is not recommended as studies show a higher likelihood of therapeutic anti-Xa levels with this approach.13,14 This is an active area of research, and these recommendations may change.
For prophylactic-dose or intermediate-dose anticoagulation, a peak anti-Xa level of 0.2 to 0.6 U/mL is generally accepted as the target. For therapeutic-dose, a peak anti-Xa level of 0.6 to 1.2 U/mL is generally accepted as the therapeutic range. This blood draw must be collected 4 hours after the third dose.
CASE 2 continued Anticoagulation considerations nearing delivery
The patient is now at 36 weeks’ gestation, and she asks, what should be done regarding her anticoagulation prior to delivery?
What would be an appropriate approach?
Traditionally, patients were transitioned to UFH at 36 weeks and allowed to present in spontaneous labor to increase the likelihood of neuraxial anesthesia. The alternative is to continue prophylactic-dose LMWH until a scheduled delivery. While the SOAP guidelines establish the timeframe that is safe to proceed with neuraxial anesthesia, there is variation in practice, so consider discussing this with your anesthesia providers.
SOAP considers prophylactic-dose UFH to be 5,000 U 2 to 3 times per day. In this setting, neuraxial anesthesia can be placed more than 4 to 6 hours from the last dose.17 But due to the pharmacokinetics of pregnancy, ACOG recommends 10,000 U in the third trimester.8 This dose is considered intermediate-dose by SOAP, and 12 hours or longer plus a normal activated partial thromboplastin time (aPTT) or undetectable anti-Xa level are required prior to neuraxial anesthesia. This is the same time allowed for prophylactic-dose LMWH without lab work. Prophylactic-dose LMWH is considered to be enoxaparin 40 mg or less daily or 30 mg twice daily, and dalteparin 5,000 U daily. For therapeutic-dose LMWH or UFH, 24 hours or more from last dose is recommended prior to neuraxial anesthesia. For intermediate-dose LMWH, data are limited to recommend anything between 12 and 24 hours.17
In my practice, we favor a shared decision-making approach with patients. We discuss the likelihood of labor prior to 39 weeks based on a patient’s history, the importance of neuraxial anesthesia to the patient, and the importance of the number of daily injections. Most patients continue enoxaparin until a scheduled induction, and they are instructed to skip their dose if labor symptoms begin. Patients at high risk for preterm delivery can be transitioned to heparin earlier than 36 weeks. ●