The process of making a clot involves a lot of steps. One of the steps involves a protein called thrombin. Heparin acts on thrombin to keep blood from clotting. A technique has been developed to measure the blood's ability to generate thrombin. The bloods's ability to generate thrombin is measured by a thrombin generation curve (TGC). This curve would be very helpful to know when choosing the dose of heparin. We haven't found any studies using TGC in babies less than a month old.