Use of high intensity adjusted dose low molecular weight heparin in women with mechanical heart valves during pregnancy: a single-center experience.

The use of standard dose low molecular weight heparin (LMWH) to anticoagulate women with mechanical valves in pregnancy is associated with morbidity and mortality. We conducted a prospective audit of the use of adjusted dose high intensity LMWH in 12 pregnancies in 11 women with prosthetic heart valves. LMWH +/- low-dose aspirin was started at therapeutic-dose with monitoring of anti-Xa levels to achieve a target level of 1.0-1.2 IU/mL (0.8-1.2 in the first 3/12 pregnancies). This necessitated a mean increase in the dose of LMWH of 54.4% (SD+/-33.2) over initial dose. Eleven of 12 pregnancies resulted in live births, with one intrauterine fetal death at 37 weeks. One non-fatal valve thrombosis occurred at 26 weeks gestation associated with subtherapeutic anti-Xa levels. Three patients experienced major bleeding. This regime provides a therapeutic option for women with mechanical heart valves during pregnancy, provided anti-Xa levels are kept within the target range. These patients require close surveillance for bleeding and thrombotic complications within a multi-disciplinary setting.