Prophylactic dosing adjustment in pregnancy based upon measurements of anti-factor Xa levels

Objective. To determine the necessity for monitoring of anti-factor Xa levels in pregnant women taking low molecular weight heparin (LMWH). Study design. A review of a hematological database with chart review was undertaken to identify patients on LMWH. Levels were drawn monthly. They were considered suboptimal if prophylactic and therapeutic doses of LMWH had an anti-Xa value < 0.2U/mL and 0.6U/mL, respectively. Variables of interest included age, parity, thrombophilias, and antiphospholipid antibody syndrome. Results. Of 30 patients, three required therapeutic-dose LMWH and 27 were on prophylaxis. Sixty-six percent on a therapeutic dose required a dose change, whereas 11% on a prophylactic dose were changed (p = 0.013). None of the variables were predictive of a need for change. One thromboembolic event was noted while on prophylactic-dose LMWH. Conclusions. No single variable is predictive of a need for dose change. Patients on a therapeutic dose were more likely to need change.