F2 and Rare hereditary thrombophilia: Estimated absolute VTE risks, calculated using the provided odds ratios and a background incidence of VTE during pregnancy of approximately 1/1000 deliveries, suggest a low thrombosis risk (0.5–1.2 % of affected pregnancies) for most of the inherited thrombophilias, except perhaps for homozygous carriers of the factor V Leiden or the prothrombin mutations, where the risk estimate is approximately 4 % (Table 5).