Thromboelastography shows Thromboprophylaxis following Caesarean Section need not be continued after 5 days for women at Moderate Risk of Thromboembolism Helena Maybury 1, Robert Smith 1, David Taylor 1, Sue Pavord 2, Jason Waugh Reproductive Sciences Section, Department of CSMM, University of Leicester, Leicester, LE2 7LX, UK 2. Department of Haematology, Leicester Royal Infirmary, Leicester, LE1 5WW, UK Introduction. Thromboembolic disease remains the leading cause of maternal mortality in the UK and the USA. Figures from the UK triennial report of maternal deaths show that 33% of all direct maternal deaths are due to thromboembolic (TE) disease. In the puerperium women are more likely to die of this disease than any other, even treated deep vein thrombosis is associated with significant morbidity with post thrombotic syndrome occurring in up to 80% of cases. It is widely accepted that caesarean section significantly increases the risk of thromboembolism, with the significant endothelial injury, prolonged immobility and reactive thrombocytosis associated with surgery, and this has been estimated to be between 4 and 20 times that following normal vaginal delivery. The response to this has been the implementation of risk assessment and the increasing use of thromboprophylaxis following delivery by caesarean section. Objective. To determine the time course for blood clotting mechanisms to return to pre-pregnancy levels in low and moderate risk women, following a caesarean section using thromboelastography (TEG). Methods. 28 women delivered by caesarean section were recruited. Citrated blood samples were collected at weekly intervals for 10 weeks and analysed by thromboelastography. All women were stratified into groups according to their risk of thromboembolic disease defined in guidelines produced by the Royal College of Obstetricians and Gynaecologists. Those in the moderate risk group (n=22) received thromboprophylaxis with low molecular weight heparin for 5 days post operatively. Three thromboelastographic parameters were analysed, Reaction time (time taken to initialise clot formation), Maximum Amplitude (maximum strength of the clot formed) and Coagulation Index which is a value derived from 4 parameters which define clot formation. A citrated blood sample was obtained from a control group of 108 non-pregnant women. This group was less than 40 years of age, not taking hormonal contraception or regular prescription medication and all of whom had previous normal pregnancies and birth outcomes. Results * * * * * * * * Δ ♦ ♥ *= p< Δ= p<0.001 ♦=p<0.005 ♥=p<0.01 In the immediate postoperative period a significant hypercoagulable state was demonstrated by a reduction in Reaction time (time to initialise clot formation) (p< ) and an increase in the Maximum Amplitude (maximum strength of clot) (p< ) and Coagulation Index (p< ) compared to non-pregnant controls. By the 21 st post-operative day the Reaction time does not differ from the non-pregnant controls (p=0.37) but the maximum amplitude and coagulation index remain significantly raised. (p<0.05, p<0.01). By the 28 th post-operative day none of the three parameters differ from the non- pregnant female controls. Sub-group analysis was performed comparing the women who were low risk for TE disease who did not receive thromboprophylaxis with LMWH with the women who were moderate risk for TE disease and received LMWH for 5 days. There were no differences between low and moderate risk women at any time in the post-natal period of 10 weeks. Conclusion. Longitudinal TEG analysis demonstrates the resolution of the hypercoagulable state after caesarean section by the 28 th post- operative day. We hypothesise that low molecular weight heparin thromboprophylaxis renders moderate risk women equivalent to low risk women in the first 5 days following caesarean section. Following this, when the thromboprophylaxis has been discontinued, the groups continue to have the same TEG profiles.