Ultrasound examination is now considered as part of almost every clinic setting. The creation of an image from sound is achieved in three steps: producing a sound wave, receiving echoes, and interpreting those echoes. The four different modes of ultrasound used in medical imaging are: A-mode, B-mode, M-mode and Doppler mode. The Doppler frequency shift information can be displayed graphically in various ways that include color Doppler (directional Doppler), power Doppler, and spectral (pulsed) Doppler. The different modes of Doppler waves include: Continuous-wave Doppler (CW) and Pulsed-wave Doppler (PW). The blood flow measurements are performed by calculation of velocity, calculation of absolute flow and flow waveform analysis. Despite its impressive safety record of ultrasound to date, the intensity (or acoustic output) level of ultrasound used to scan the fetus in utero has increased almost eightfold over the level that was allowed in the early 1990s.