Dose Adjusting Enoxaparin Thromboprophylaxis Dosage According to Anti-factor Xa Plasma Levels Improve Pregnancy Outcome

The risk of venous thromboembolism increases in pregnancy. Thrombophilia whether genetic or acquired, is a hypercoagulable disorder that may increase the risk of venous thromboembolic events. Clinically, these events are presented as maternal deep vein thrombosis and pulmonary emboli. Thrombophilias are also associated with adverse fetal outcomes including intrauterine growth restriction, intrauterine fetal death, severe preeclampsia, placental abruption and recurrent abortions.

Pregnant women who experienced one or more of the above complications are advised to be examined for the presence of the genetic or the acquired form of thrombophilia.

Low molecular weight heparin prophylaxis, an anticoagulant, is advised for pregnant women with a history of thromboembolism, and many experts recommend prophylaxis for pregnant patients with a known thrombophilia and history of adverse pregnancy outcomes associated with these hypercoagulable states.

Physiologic changes in normal pregnancy, including weight gain, increased renal clearance and volume of distribution, may decrease the availability of low molecular weight heparin (Enoxaparin or Dalteparin), or produce a less predictable response in pregnant women compared with nonpregnant women. There are no clear recommendations for use of prophylactic low molecular weight heparin in pregnancy. Clinicians tend to use doses suggested for nonpregnant patients. Regarding pregnant patients taking enoxaparin or dalteparin, the American College of Obstetricians and Gynecologists states that "because of the lack of data regarding adequate dosing during pregnancy, anti-factor Xa levels may be monitored".

Two recently published studies demonstrated that plasma anti-factor Xa levels during pregnancy were lower than expected, indicating that many pregnant patients may receive a subprophylactic dosing.

Our objective is to check pregnancy outcome among thrombophilic women treated with an adjusted enoxaparin thromboprophylaxis dosage according to anti-factor Xa plasma levels compared to women with fixed dosage.