Limited data exist on thrombophilia and the risk of venous thrombosis (VT) during pregnancy and postpartum. The objectives of the present study were to investigate the role of haemostatic risk factors for pregnancy-related VT and their phenotypic expression in deep-vein thrombosis (DVT) and pulmonary embolism (PE). Total 313 cases with objectively verified first time VT and 353 controls were selected from a source population of 377,155 women with 613,232 pregnancies. The adjusted odds ratio (aOR) for pregnancy-related VT was 1.7 (95% confidence interval [CI] 1.1-2.8) for women with factor VIII >90th percentile. The aOR for VT for endogenous thrombin potential and D-dimer values >90th percentiles were 1.8 (95% CI 1.1-3.0) and 2.1 (95% CI 1.3-3.3), respectively. Factor IX >90th percentile or free protein S ≤the 5th percentile increased the risk for PE, and the aORs were 2.4 (95% CI 1.1-5.0) and 3.1 (95% CI 1.3-7.2), respectively. Women carrying the factor V Leiden (F5 rs6025) polymorphism, or who had reduced sensitivity to activated protein C (aPC) in the absence of F5 rs6025, had increased risk for DVT, with unadjusted ORs 7.7 (95% CI 4.7-12.7) and 3.5 (95% CI 2.2-5.4), respectively. Women with a history of pregnancy-related VT showed activation of coagulation and had elevated factor VIII. Furthermore, high levels of factor IX and low levels of free protein S were associated with increased risk for PE, whereas aPC resistance and F5 rs6025 were risk factors for DVT and not PE.