In this work we investigate the influence of V-shaped pits on the growth of GaInN-GaN MQW's by TEM and x-ray diffraction measurements. We have grown different MQW's using low-pressure MOVPE and studied the influence of the number of QW's as well as of the depth of V-shaped pits. During the growth of the samples a material transport takes place from the pits to the c-plane. We show that the thickness of the GaInN QW's and of the GaN barriers is increased due to material transport. With increasing number of quantum wells the diameter of the pits increases, which leads to a super linear increase of these thicknesses. We present a model which describes the change in thickness due to material transport. Another consequence of material transport is a lateral fluctuation in thickness with a characteristic length on the order of the distances between the dislocations.