Pregnancy-related venous thromboembolism is the most common cause of maternal death and a significant cause of maternal morbidity. The factor V Leiden (FVL) mutation is the most common known genetic factor that predisposes to thrombosis. How does obstetric management differ regarding a heterozygous or homozygous carrier? When should anticoagulation be used, and at what dose? In this session we will review data from the SMFM, RCOG, and the ACOG practice bulletin 197.