Summary

Increased thromboembolic events occur in women withmechanical prosthetic valves during pregnancy, and selecting aneffective and safe anticoagulant is still a challenge. Low molecularweight heparin (LMWH) is a promising alternative, but arecent warning and label change about its use in patients withmechanical prosthetic valves has caused confusion among physicians.The aim of the present study was to review the risks ofmaternal and fetal complications with mechanical heart valvestreated with LMWH during pregnancy.We performed a reviewof the current medical literature through MEDLINE andEMBASE (1989 to 2004).Additional data sources included abstractproceedings, and reference lists of selected articles.Among 81 pregnancies in 75 women, the proportion of valvethrombosis was 8.64% (7/81; 95% CI, 2.52%-14.76%). The frequency of overall thromboembolic complication (TEC) was12.35% (10/81; 95% CI, 5.19%-19.51%). Nine of ten patientswith TEC received a fixed dose of LMWH and two of thesereceived a fixed low dose of LMWH. Among 51 pregnancieswhose anti-factor Xa levels were monitored, only one patientwas reported to have a thromboembolic complication.The frequencyof live births with LMWH was 87.65% (95%CI, 80.49%-94.81%). In pregnant women with mechanical heart valves,LMWH appears to be a suitable option to a vitamin K antagonist.The use of LMWH warrants monitoring and appropriatedose adjustments to maintain a 4-6 hr post-injection anti-factorXa level at a minimum of 1.0 U/ml to decrease the incidence ofTEC.