Prospective evaluation of coagulation activation in pregnant women receiving low-molecular weight heparin.

Pregnancy is a major risk factor for venous thromboembolism (VTE), and low-molecular weight heparin (LMWH) seems to be safe and effective in pregnant women. Normal pregnancy is accompanied by a state of hypercoagulability, indicated by an increase in markers of coagulation activation. In a prospective cohort study, we followed 61 women who received LMWH thromboprophylaxis throughout pregnancy because of a history of VTE, hereditary thrombophilia and/or previous pregnancy-related complications. The control group consisted of 113 healthy pregnant women without antithrombotics. D-Dimer, prothrombin fragment F1+2 (F1+2) and the resistance to activated protein C (APC-ratio) were measured in all women during the first, second and third trimester. Patients and controls did not significantly differ with regard to baseline characteristics and pregnancy outcome. A (recurrent) VTE was seen in one patient despite LMWH. D-Dimer levels significantly increased among patients and controls during pregnancy (p < 0.0001), and were significantly higher among patients compared with the controls (p <0.0001) [395 ng/ml (95% CI 340-458) and 249 ng/ml (95%CI 234-266); 710 ng/ml (95% CI 602-838) and 475 ng/ml (95% CI 431-523); 1089 ng/ml (95% CI 931-1273) and 822 ng/ml (95% CI 741-911); respectively]. Levels of F1+2 significantly increased while the APC-ratio significantly decreased during pregnancy among patients and controls. Despite LMWH, pregnancy is accompanied by a substantial activation of the coagulation system.