The frequency of planar defects, the average dislocation densities, and coherent domain size in epitaxial GdBa2Cu3O7-x high Tc thin films, with altering CuO2 and CuO planes, are measured by fitting full widths at half maximum values of 00l type reflections using a model function based on intensity distribution configurations in reciprocal space. The reduction of the dislocation density during oxygenation seems to be an unavoidable condition to obtain superconductivity in GdBa2Cu3O7-x thin films. [ABSTRACT FROM AUTHOR]