Thrombin generation post elective caesarean section: Effect of low molecular weight heparin

Introduction: Caesarean section (CS) is a significant risk factor for venous thromboembolism. Low molecular weight heparin (LMWH) is commonly used for thromboprophylaxis post emergency caesarean delivery. However, no consensus exists regarding LMWH thromboprophylaxis following elective caesarean section. Measures of thrombin formation may indicate the full anticoagulant activity of LMWH in this setting. Materials and methods: Anti-Xa, tissue factor pathway inhibitor (TFPI), thrombin anti-thrombin complex (TAT) and endogenous thrombin potential (ETP) were measured in twenty healthy women who received 4,500 IU tinzaparin 6 hours post CS (CS1), twenty women who received 4,500 IU tinzaparin at 10-12 hours post delivery (CS2) and twenty women post spontaneous vaginal delivery (SVD). Results: Prior to initiation of LMWH, TAT levels at 6 hours post delivery were significantly higher in the CS1 and CS2 groups than the SVD group (P < 0.002); TAT levels were significantly reduced up to 24 hours post LMWH treatment despite declining anti-Xa levels (P < 0.001). In CS1, peak thrombin and ETP were significantly reduced following LMWH prophylaxis (P < 0.0001; P < 0.002) and reverted to pre-delivery levels 10 hours post LMWH. TFPI levels mirror anti-Xa levels during the 24 hours following LMWH treatment in CS1 group with peak levels coinciding with peak anti-Xa levels 4 hours post injection. Conclusion: In women post caesarean section, anti-Xa levels do not reflect the full anticoagulant effects of LMWH. In-vivo thrombin production (TAT) is effectively reduced even when anti-Xa levels are negligible. LMWH thromboprophylaxis in this healthy cohort of patients appears to have a sustained effect in reducing excess thrombin production post elective caesarean section.