2D, 3D, 4D In clinical work, I am often asked, especially during mid pregnancy, doctor, I want to do 4D ultrasound. Every time, they explain that 4D ultrasound is not the same as prenatal screening ultrasound. Prenatal screening is certified and is a tertiary prevention. The concept of 4-dimensional ultrasound is only the ultrasound dimension. It does not exclude for-profit hospitals from making a big deal out of 4D ultrasound for publicity purposes. My understanding of the ultrasound dimension: two-dimensional is flat, three-dimensional is three-dimensional, four-dimensional is on top of the three-dimensional added the dimension of time, it is dynamic. You can use 4-dimensional to understand the heart condition. All three dimensions, four dimensions are on top of two dimensions, do not be superstitious four dimensions.