Use of Antithrombotic Agents During Pregnancy: Efficacy of Anticoagulants for the Prevention and Treatment of VTE During Pregnancy
There is a paucity of data about the efficacy of anticoagulants for the prevention and treatment of VTE during pregnancy. Accordingly, the recommendations about their use during pregnancy is based largely upon extrapolations from data from nonpregnant patients, from case reports, and from case series of pregnant patients. Based upon the safety data, heparin is the drug of choice for the prevention and treatment of VTE during pregnancy.
The results of a large randomized trial in nonpregnant patients have shown that full-dose IV heparin, followed by 3 months of ql2h subcutaneous heparin, in doses adjusted to prolong a midinterval APTT into the therapeutic range (adjusted-dose subcutaneous heparin), is safe and effective. Therefore, it seems reasonable to extrapolate these results to pregnant patients with DVT and pulmonary embolism (PE) and use IV heparin followed by at least 3 months of adjusted-dose subcutaneous heparin. In addition, subcutaneous LMWH is likely to be effective and safe for the treatment of acute VTE. Although dosing during pregnancy is unclear, we use weight-adjusted doses that are increased as the woman’s weight increases. If available, measurement of anti-factor Xa levels approximately 4 h after injection and adjusting to a level of approximately 0.5 to 1.2 U/mL should be performed.
Pregnant women with previous VTE are probably at increased risk for recurrent VTE, but the magnitude of the risk is unknown. It is likely that the risk of recurrence is higher in women with previous idiopathic VTE than in women who develop VTE in association with a transient risk factor. It is not clear whether women who develop VTE in association with previous pregnancy are at a relatively higher risk of recurrence. Based on the current state of knowledge, there are two general approaches to pregnant patients with previous VTE: (1) active prophylaxis with heparin or LMWH; and (2) clinical surveillance. Subcutaneous heparin, 5,000 U ql2h, is effective and safe for the prevention of VTE in high risk nonpregnant patients, and its use has been recommended in pregnant patients.