Objective: To compare the adequacy of venous thromboembolism prophylaxis based on anti-Xa concentrations between weight-based enoxaparin dosing and body mass index (BMI)-stratified dosing in morbidly obese women after cesarean delivery.
Methods: A prospective sequential cohort study of women with BMIs of 40 or greater who underwent cesarean delivery was conducted. Participants received either weight-based or BMI-stratified enoxaparin dosing to prevent venous thromboembolism formation. The weight-based regimen was 0.5 mg/kg of enoxaparin every 12 hours. In the BMI-stratified regimen, women with BMIs of 40-59.9 received 40 mg enoxaparin every 12 hours and women with BMIs of 60 or greater received 60 mg every 12 hours. The primary outcome was an anti-Xa concentration in the adequate thromboprophylaxis range (0.2-0.6 international units/mL). Secondary outcomes included enoxaparin dosage, timing of dosing and anti-Xa concentration, estimated surgical blood loss, postoperative changes in hemoglobin and platelets, wound hematoma, and adverse reactions to enoxaparin. Univariate analysis was used to compare dosing regimens.
Results: Forty-two morbidly obese women received weight-based enoxaparin, and 43 received BMI-stratified dosing. Anti-Xa concentrations were significantly higher in the weight-based group compared with the BMI-stratified group (0.29±0.08 international units/mL compared with 0.17±0.07 international units/mL, P<.001). Thirty-six participants (86%) on weight-based dosing had anti-Xa concentrations within the prophylactic range compared with 11 (26%) on BMI-stratified dosing (P<.001). No participant had an anti-Xa concentration of 0.6 international units/mL or greater, the therapeutic threshold for venous thromboembolism prophylaxis.
Conclusion: In morbidly obese women after cesarean delivery, weight-based dosing of enoxaparin for venous thromboembolism prophylaxis is significantly more effective than BMI-stratified dosing in achieving adequate anti-Xa concentrations.
Level of evidence: II.