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When it comes to a traditional scan (2D scan), the ultrasound machine sends out sound waves at a high frequency (approx. 2-8 Mhz) into the abdomen with the help of a transducer. It is the same transducer that picks-up the echoes, which are thrown back with the soundwaves after it has hit the different parts of the fetus.

These echo signals are then converted into different computer signals depending on how long it takes for the echoes to be registered by the transducer.

On the screen, it is possible to see cut-picture of an organ, for example, the fetus head in 2 dimensions (2D), which equivalent to the length and width. If the depth is measured, then the transducer is turned 90 degrees.