1000 U Ihr or 15 to 20 U Ikg/hr. his infusion rate is titrated to achieve an aPTT 1.5 to 2.5 times control values (Brown, 2010; Linnemann, 2016). Intravenous anticoagulation is maintained for at least 5 to 7 days, after which treatment is converted to subcutaneous heparin to maintain the aPTT to at least 1.5 to 2.5 times control throughout the dosing interval. For women with lupus anticoagulant, aPTT does not accurately assess heparin anticoagulation, and thus anti-factor Xa levels are preferred.
The duration of full anticoagulation varies, and no studies have defined the optimal duration for pregnancy-related thromboembolism. In nonpregnant patients with TE, evidence supports a minimum treatment duration of 3 months (Kearon, 2012). For pregnant patients, the American College of Chest Physicians recommends anticoagulation throughout pregnancy and postpartum for a minimum total duration of 3 months (Bates, 2012). Lockwood (2012) recommends that full anticoagulation be continued for at least 20 weeks followed by prophylactic doses if the woman is still pregnant. Prophylactic doses of subcutaneous UFH can range from 5000 to 10,000 U every 12 hours titrated to maintain an anti-factor Xa level of 0.1 to 0.2 U/mL, measured 6 hours after the last injection. If the TE occurs during the postpartum period, Lockwood (2012) recommends a minimum of 6 months of anticoagulation treatment.
This is a family of derivatives of unfractionated heparin, and their molecular weights average 4000 to 5000 daltons compared with 12,000 to 16,000 daltons for conventional heparin. None of these heparins cross the placenta, and all exert their anticoagulant activity by activating antithrombin. The primary diference is their relative inhibitory activity against factor a and thrombin. Specifically, UFH has equivalent activity against factor a and thrombin, but LMWHs have greater activity against factor a than against thrombin. They lso have a more predictable anticoagulant response and fewer bleeding complications than UFH because of their better bioavailability, longer half-life, dose-independent clearance, and decreased interference with platelets (Tapson, 2008). hese LMWH compounds are cleared by the kidneys and must be used cautiously when there is renal dysunction.
Several studies have shown that TE is treated efectively with LMWH (Quinlan, 2004; Tapson, 2008). Using serial venograms, Breddin and associates (2001) observed that these compounds were more efective than UFH in reducing thrombus size without increasing mortality rates or major bleeding complications. Several diferent treatment regimens using adjusted-dose LMWH for treatment of acute TE are recommended by the American College of Obstetricians and Gynecologists (2017b,c) and are listed in Table 52-5.