There are differences in the types of ultrasound scan done in pregnancy. The standard is a 2D ultrasound or 2 dimensional image. In recent years has been replaced with the new 3D ultrasound scan or three dimensional images and now 4D ultrasound scan (movement). 2D ultrasound is the traditional method used for years. They provide flatter, two-dimensional, black and white images of your baby,very helpful in diagnosis.