Ultrasound is routinely used in assisted reproductive technology for monitoring of follicular growth, oocyte retrieval and embryo transfer, as well as for the assessment of early embryonic development in the first 5 to 8 weeks of pregnancy. Ultrasound is a form of energy, which will affect live tissues it traverses (bioeffects) by being partially transformed into heat (thermal effect) and by alternating positive and negative pressures (nonthermal or mechanical effect). In the United States 2 indices (thermal and mechanical index) must be displayed on-screen to provide the clinicians an indication of possible thermal and nonthermal changes. The thermal index and mechanical index should be kept below 1. The use of Doppler involves much higher levels of energy than B-mode gray scale 2-dimensional or 3-dimensional and special precautions are recommended when utilizing this modality. Information on susceptibility of the oocyte, prefertilization or postfertilization and the possible vulnerability of the very early fetus to such energy is very scarce. Data on whether there is a cumulative effect or an effect of recurrent exposure (eg, oocyte growth follow-up) do not exist. Ultrasound should be used only when medically indicated, for the shortest time and at the lowest intensity compatible with accurate diagnosis, especially when performing Doppler studies. In addition, because of lack of knowledge regarding bioeffects and safety among clinicians, educational effort is needed.