Choice of anticoagulant therapy for a mechanical prosthetic valve during the 1^st trimester of pregnancy

VKA: vitamin K antagonist; INR: international normalized ratio; SC LMWH: subcutaneous low molecular weight heparin; UFH: unfractionated heparin; IV: intravenous; aPTT: activated partial thromboplastin time.
* Refer to UpToDate content on the maternal and fetal risks associated with various types of anticoagulants.
¶ Refer to UpToDate content on therapeutic targets for VKA for mechanical prosthetic valves. Although therapeutic VKA therapy during the 1^st trimester is an option for some clinical settings, some pregnant women in these settings will choose to avoid the fetal risks of VKA therapy and will opt for SC LMWH (administered at least twice daily with anti-Xa monitoring) despite the greater risks of prosthetic valve thrombosis and thromboembolism.
Δ For patients taking high-dose VKA, some clinicians offer the option of continued VKA during the 1^st trimester after fully informed consent.
◊ When a decision is made to switch to LMWH, VKA should be discontinued and dose-adjusted SC LMWH started (at least twice daily; along with daily low-dose aspirin) once pregnancy is confirmed and ideally before the 5th week of gestation. A plan should be made prior to conception on how this change in therapy will be performed (including potential hospitalization for close monitoring during the transition). Target anti-Xa activity 1.0 to 1.2 units/mL for mitral valve prosthesis and 0.8 to 1.0 units/mL for aortic valve prosthesis at 4 to 6 hours postdose). We also suggest checking trough activity 30 minutes or less prior to the next dose (proposed minimum trough level of 0.6 units/mL), although the efficacy and safety of this approach have not been established. Refer to UpToDate content on administration of LMWH.
§ If LMWH is unavailable due to resource limitations, inpatient dose-adjusted continuous IV infusion of UFH (with targeted aPTT 2 to 2.5 times control or anti-Xa activity 0.3 to 0.7 units/mL) plus low-dose aspirin is a potential option, although the efficacy and safety of this treatment over weeks are uncertain, given difficulties in monitoring IV UFH, the limited efficacy of UFH in this setting, and the risk of infection.