[Antithrombin III assay using a chromogenic substrate in newborns].

The assay of antithrombin III activity (AT-III) was performed by chromogenic synthetic substrate in 42 full-term newborns, 1 to 7 days aged. AT-III levels were lower than normal adults in the first day of life and lessened again in the 3rd day. After this period the levels of AT-III rose slowly and in the 7th day were about half the concentration of adults.