- Venous thromboembolism (VTE) is a leading cause of morbidity and mortality in pregnant women. Enoxaparin is a low-molecular-weight heparin used during pregnancy to treat or prevent VTE. In this study, we compare anti-factor Xa peak levels in pregnant and non-pregnant women, and explore the association between anti-factor Xa (AFXa) peak levels and possible predictive parameters. Pregnant and non-pregnant patients received a therapeutic dose of enoxaparin every 12 h and three steady-state AFXa peak levels at 4-week intervals were collected. Sixty-eight patients (36 pregnant and 32 non-pregnant women) were enrolled. AFXa peak levels within therapeutic range (0.6-1.0 IU/ml) were achieved in the first measurement in 14 (38.9%) pregnant women compared to 21 (65.6%) non-pregnant women (p = 0.028). In the second anti-factor Xa measurement, 20 (55.6%) compared to 25 (78.1%) were within the reference interval (p = 0.008). Similar results were seen with the third measurement 20 (55.6%) compared to 26 (81.3%) (p = 0.003). In a mixed-effect repeated-measures model, pregnancy was associated with AFXa peak level (Mean difference = - 0.177; 95% CI - 0.349 to - 0.005, p = 0.044). These findings suggest that further evaluation of a strategy involving more frequent monitoring of achieved AFXa levels could result in more effective anticoagulation.