Diagnostic ultrasound is a form of energy that has the potential for effects in tissues (bioeffects). The 2 most likely mechanisms are heating and cavitation. The thermal index (TI) expresses the potential for rise in temperature. The MI indicates the potential for the ultrasound to induce inertial cavitation. Scarce data exist regarding instrument's acoustic output for routine ultrasound examinations. Data collected during routine ultrasound examinations (first trimester for viability, nuchal translucency, anatomy surveys including 3-dimensional/4-dimensional studies and growth studies) show that "gray-scale" B-mode ultrasound is associated with a negligible rise in TI. However, Doppler studies show significantly higher levels of TI, which can reach 1.5 and above.