In regions where LMWH is unavailable or cost-pro- hibitive, or if anti-Xa levels cannot be monitored, continuous infusion of UFH can be used as an alternative to LMWH during the first trimester for women who require a warfarin dose of >5 mg/d.37 If UFH is used during the first trimester, the dose should be adjusted to maintain an aPTT 2 times control. There are several disadvantages to UFH compared with LMWH: Women are at greater risk for line infections, osteoporosis, and hepa- rin-induced thrombocytopenia, so UFH should be reserved for situations where dose-adjusted LMWH is not feasible.10 Intermittent subcutane- ous injection of UFH is not an acceptable alterna- tive because it is associated with prohibitive rates of valve thrombosis.42 UFH is associated with very high rates of valve thrombosis, stroke, and death in pregnant women with mechanical heart valves during the second and third trimesters.3,4,43 11. In carefully selected women with thrombosis of a mechanical heart valve during pregnancy, low- dose, slow-infusion, tissue-type plasminogen acti- vator (tPA) can be an alternative to surgical valve replacement. Women who are optimal candidates are hemodynamically stable and have obstructive prosthetic valve thrombosis, valve thrombosis with embolic complications, or nonobstructive valve thrombosis with a thrombus >10 mm.44 Given the high rates of fetal loss with cardiac surgery during pregnancy, thrombolysis is an attractive alterna- tive for appropriately selected, hemodynamically stable women with mechanical valve thrombosis. 12. Although the teratogenicity of warfarin is high- est during the first trimester, there is still a risk of pregnancy loss or fetal hemorrhage when warfarin is taken during the second and third trimesters. Therefore, after appropriate counsel- ing, some women may choose to avoid warfarin entirely throughout pregnancy. For these women, dose-adjusted LMWH throughout pregnancy is the safest alterative. 