Ultrasound in Reproductive Medicine: Is It Safe?

Abstract

Many technologies have burgeoned and vastly expanded in obstetrics and gynecology over the last half century. Among them, assisted reproductive technology (ART) and ultrasound may be the most widely used in daily practice. 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 (TI) and the mechanical (MI) indices, give the end user an indication of possible thermal and nonthermal changes occurring in real time during the ultrasound scan. While no harmful effects have been described in epidemiological studies in humans, some deleterious results have been demonstrated in animals. Furthermore, most epidemiological studies were performed before 1992, a time when maximal energy (acoustic) output for fetal studies was allowed to be increased and data available on machines used presently are limited. While intensities produced by B-mode, grayscale 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 more vulnerable to external influences or insults than later in pregnancy. Information on susceptibility of the ovum, pre- or postfertilization, is even scarcer. In addition, knowledge regarding bioeffects and safety of ultrasound by clinical end users is grossly inadequate. While it appears that in vivo exposure to ultrasound at spatial average intensities below 1 W/cm 2, which is arguably 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. Further prospective studies on ultrasound safety in ART and pregnancy are highly recommended.