The appearance of periodically distorted director structures in pretilted nematic slabs with rigid boundary conditions above the Fréedericksz transition is determined as a function of the Frank elastic constant ratios K(2)/K(1), K(3)/K(1), and the pretilt angle. It is found that the periodically distorted state can be reached either directly from the undistorted state on increasing the magnetic field or indirectly through the homogeneously distorted state. A new threshold field for the transition undistorted state, homogeneously distorted state was found for specific ranges of the Frank elastic constant ratios K(2)/K(1), K(3)/K(1), and the pretilt angle.