Anticoagulant therapy in pregnant women with mechanical prosthetic heart valves: no easy option.

The choice of anticoagulant agent for pregnant women with mechanical prosthetic heart valves introduces a clinical dilemma for women and the clinicians caring for them. Options include continuing oral anticoagulants (OAC) such as warfarin throughout pregnancy, switching from warfarin to unfractionated heparin or low molecular weight heparin (LMWH) in the first trimester then back to warfarin until close to delivery or taking unfractionated heparin or LMWH throughout pregnancy. The dilemma is that warfarin is the most effective a preventing maternal thromboembolic complications but causes significant fetal morbidity and mortality; unfractionated heparin and in particular LMWH have good fetal outcomes but the risk of thromboembolic complications is high. What is considered to be an "acceptable level" of risk to mother and infant may differ from one clinician to another and of equal importance, it may also differ from one woman to the next. An unbiased discussion of the pros and cons of each option is required to allow women to make and informed and confident choice in this very difficult clinical situation.