Ultrasound in reproductive medicine: is it safe?

Ultrasound is a form of energy with effects in tissues it traverses (bioeffects). The major bioeffects are a rise in temperature (thermal effects) and some effects secondary to the alternating positive and negative pressures of the ultrasound wave (nonthermal or mechanical effects). Two on-screen indices, the thermal index (TI) and the mechanical index (MI), give the end user an indication of possible thermal and nonthermal changes occurring in real time during the ultrasound scan. No harmful effects have been described in epidemiological studies in humans, but some deleterious results have been demonstrated in animals. While intensities produced by B-mode, gray-scale ultrasound are, most likely, safe, the use of Doppler involves much higher levels of energy. In addition, the very early fetus is known to be very vulnerable to external influences or insults. Information on susceptibility of the ovum, pre- or postfertilization, is virtually inexistent. In addition, knowledge regarding bioeffects and safety of ultrasound by clinical end users is grossly inadequate. In vivo exposure to ultrasound at spatial average intensities below 1 W/cm2, which is, arguably, almost always the case in ART as well as early gestation, does not adversely affect oocytes/embryos/fetuses. It is advocated to utilize ultrasound only when medically indicated, for the shortest time and at the lowest intensity compatible with accurate diagnosis. The TI and MI should be kept below 1. Further prospective studies on ultrasound safety in ART and pregnancy are highly recommended, as is education of the end users.