Region growing has become a popular method for 3D segmentation. Starting from a seed, this approach allows one to extract a region by merging all its neighbors and comparing the extracted region to a reference. Here, we present an alternative approach to constrain the evolution of the region growing method in respect to a fixed reference shape. This approach is based on a shape description by the Tchebichef moments. The evolution equation minimizes a function that represents the distance between the evolving region and the reference shape. Experimental results show the ability of our method to drive the segmentation towards a desired shape in 2D and 3D data. Finally, we apply our shape prior conjointly to a bimodal segmentation functional, showing its benefits on segmentation results.