The risk of poor fetal outcomes is also high, with increased rates of spontaneous abor- tion, fetal death, fetal hemorrhage, and teratogenic- ity related to VKAs. For women with mechanical heart valves, the maternal mortality rate remains >1%. More than one-third of women with mechanical heart valves have a serious maternal or fetal complication during All women with mechanical heart valves require uninterrupted therapeutic anticoagulation throughout pregnancy. The choice of anticoagulation strategy is challenging because there are inherent trade-offs be- tween maternal safety and fetal safety. Warfarin is the most effective anticoagulant at preventing thrombotic complications, but warfarin crosses the placenta and can cause miscarriage, spontaneous abortion, war- farin embryopathy, or fetal intracranial hemorrhage. Although LMWH is not teratogenic, women with me- chanical heart valves on LMWH are at increased risk of thrombotic events, particularly when LMWH is im- properly dosed, monitored, or administered. There is no single optimal anticoagulation strategy that suits all women. There are 3 potential strategies: 1) Continue warfa- rin throughout pregnancy; 2) use heparin throughout pregnancy; and 3) use sequential therapy, with heparin during the first trimester and warfarin during the sec- ond and third trimesters (Figure 18). Recommendation-Specific Supportive Text 1. The risk of catastrophic valve failure or stroke is prohibitively high for women with mechanical heart valves who cannot take dose-adjusted and frequently monitored anticoagulation throughout 2. Much of the maternal morbidity and mortality during pregnancy occurs in women who are not receiving appropriate doses of anticoagulation because of improper administration, improper monitoring, or medication nonadherence. Women who are not able to receive therapeutic anticoagulation or do not have access to frequent monitoring and dose adjustment are at prohibi- tive risk for pregnancy.13 15 3. No anticoagulation strategy is optimally safe for both the mother and the fetus. 