1. 3-dimensional (3D) ultrasound system comprising: an extractor configured to scan a 3D ultrasound data of a fetus and to extract a side image of the fetus from the 3D ultrasound data, the side image including an NT (nuchal translucency) region of the fetus; a processor configured to detect a first edge and a second edge of the NT region included in the side image; and a controller configured to measure the thickness of the NT region based on a distance between the first edge and the second edge, wherein the processor detects the first edge of which brightness intensity is changed from a large value to a small value in the side image, and detects the second edge of which brightness intensity is changed from a small value to a large value in the side image.