Which of the following statements about oral anti-coagulants is FALSE
Oral anticoagulants inhibit the activation of factor II, VII, IX and X. These do not affect the synthesis of these factors
They interfere with an early step in the synthesis of clotting factors
Irrespective of the dose administered, their anticoagulant effect has a latency of onset of 1-3 days
Their dose is adjusted by repeated measurement of prothrombin time
They are contraindicated during pregnancy