To demonstrate that the presence and sum of the diameters of the nucleus of epiphysial ossification of long bones is effective in term pregnancy diagnosis and differentiation between term newborn premature and full-term in patients undergoing elective cesarean section. Material and Methods: Prospective analytical observational cohort study, which evaluated 52 patients treated at the Gynecology Service of Hospital Regional Docente de Trujillo in the period November 2013 to April 2014; the newborns (NB) were evaluated early term and full term. Femur, tibia, humerus: the presence, extent and summation of the nucleus bone ossification was determined. Results: The extent of distal femoral nuclei ossification (NOFD)> 4 mm as a diagnostic test for predicting 39-41 weeks gestation, has a sensitivity: 93.1% (78 to 98.1); Specificity: 34.8% (18.8 to 55.1), PPV: 64.3% (49.2 to 77.0), NPV: 80% (49 t...