Embodiments for forming multiple plane images for a target object in an ultrasound system are disclosed. A processor forms volume data indicative of the target object by using ultrasound data. The processor is configured to: set a reference plane in the volume data detect a falx contour and a contour of a cerebrum in the reference plane and an entire contour of the brain in the volume data normalize the volume data by using the falx contour, the cerebrum contour and the entire contour of the fetal brain and set multiple planes with respect to the reference plane in the volume data. The processor forms plane images corresponding to the respective multiple planes by using the volume data.
