Wasserloos A, Costa SD, Zenclussen A, et al. - The leading cause of pregnancy-related maternal morbidity and mortality is venous thrombosis. Increase in the thrombosis risk has been observed in correlation with caesarean section and blood loss, however, uncertainty remains concerning the underlying mechanisms of these prothrombotic changes. Researchers herein performed a prospective study recruiting 50 pregnant women at term undergoing elective cesarean section at University Hospital Magdeburg, Germany. Among these women, mean blood loss of 506 ml was observed. Preoperatively, total protein S was 0.63 U/ml, which reduced by 14.8% following cesarean section and nearly normalized 5 days later. Observations revealed a simultaneous deficiency of anticoagulant proteins and increase in APC resistance following peripartal blood loss. After a moderate blood loss during caesarean section, a marginal decrease in the endogenous thrombin potential (ETP) was observed. Different patterns of normalization of various coagulation proteins were revealed postpartum. The likely contributers to the thrombosis risk after postpartum hemorrhage is combined deficiency of anticoagulants and APC resistance.