Pregnancy increases the risk of venous thromboembolism (VTE). During pregnancy and a post-cesarean section, an increase in D-dimer levels can be observed. However, to date, the usefulness of the D-dimer level measurement for thrombosis in pregnant women has not been determined. We aimed to evaluate the changes in D-dimer levels after a cesarean section, the risk factors of high D-dimer levels, and enoxaparin sodium’s preventive effects on VTE. This retrospective study enrolled 160 pregnant women who underwent a cesarean section. D-dimer levels were measured on postoperative day (POD)1 and POD6. If on POD1, the D-dimer levels were ≥10 µg/mL, enoxaparin sodium was administered until POD7. Regardless of enoxaparin administration, when the D-dimer levels on POD6 were ≥10 µg/mL, lower-limb venous ultrasonography was performed. After a cesarean section, patients were screened for the following: factors causing high D-dimer levels, incidence of deep vein thrombosis (DVT), and need for enoxaparin. The median D-dimer levels on POD1 and POD6 were 7.5 µg/mL (1.1-34.1) and 4.2 µg/mL (0.02-31.4), respectively. Enoxaparin sodium was administered to 56 patients (35%). The D-dimer levels on POD6 decreased more significantly than on POD1. The median D-dimer levels in the enoxaparin administration group significantly dropped from 14.3 (POD1) to 3.9 (POD6) (<.001). The D-dimer levels on POD1 were higher in patients aged ≥35 years and with a hospitalization history of threatened preterm labor. In addition, on POD6, patients aged ≥35 years and with a high body mass index had high D-levels. Following a multivariate analysis, the elderly represent an independent factor for high D-levels. DVT was not observed. When the D-dimer levels on POD1 after a cesarean section are ≥10 µg/mL, enoxaparin reduces D-dimer levels six days after cesarean section. Moreover, patients aged ≥35 years represent an independent factor for high D-levels. These findings should be validated by further studies.