The Prothrombin Time (PT) test is carried out to check that your platelets are functioning properly and a clot is being formed at the site of injury.  The international normalized ratio (INR) is calculated from a PT result and is used to monitor the working of the blood-thinning medication (anticoagulant) warfarin to prevent blood clots. Delivery of the baby involves blood loss and thus it is important to keep the blood loss to a minimum.