Finding periodic microstructures with optimal elastic properties is usually tackled by a highly resolved, regular finite element model and solid isotropic material penalization. This procedure not only has many advantages, but also requires a comparably high computational effort and challenges in representing stresses accurately. Therefore, an isogeometric shape optimization approach is applied to the inverse homogenization problem and combined with a reconstruction procedure for nearly optimal rank-3 laminates, which provides an efficient solution strategy with more accurate stress modelling. This allows to investigate the sensitivity of optimized microstructures in terms of stress concentrations.