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The number of indications for ultrasound examination during pregnancy is rising.
The number of indications for ultrasound examination during pregnancy is rising. In addition, experts have expanded the gestational age range for which fetal ultrasound assessment is appropriate to include the first trimester. Considering the increased use of ultrasound, should clinicians heighten their concern regarding the safety of this technique? Are there ways to minimize potential risks to the fetus? What do clinicians need to know about the safety of this important imaging modality during pregnancy? The answers are not as straightforward as one might think.
This article reviews the potential impact of ultrasound on the fetus and ways through which the sonographer can minimize risk and maximize safety. A key element of this is understanding how to use the output display standard (ODS) during all obstetric ultrasound examinations. The ODS, which is displayed on screen during an ultrasound examination, provides an approximation of biologic risk generated during the exam. It is currently the safety mechanism in place for all ultrasound examinations, and the American College of Obstetricians and Gynecologists (ACOG) supports its use.1
Potential bioeffects of ultrasound
Thermal bioeffects refer to biologic changes associated with a rise in temperature in the targeted tissue.3 Although some ultrasound waves reflect off the exposed tissue and are used for the generation of images, others are absorbed by the tissue and the energy is converted into heat.3 This is important given the potential teratogenicity of fetal exposure to significant temperature elevations.4
Nonthermal bioeffects, frequently referred to as mechanical bioeffects, are biologic changes resulting from ultrasound insonation without a pathophysiologic rise in temperature. Although this concept is somewhat abstract, it nonetheless appears to be relevant in fetal ultrasound safety.5 Examples of mechanical bioeffects observed with diagnostic ultrasound include cavitation, acoustic streaming, radiation forces, and free-radical generation. The term cavitation, which is frequently encountered when investigating mechanical bioeffects, refers to the interaction between an ultrasound wave and a gas bubble.5 Ultrasound waves can cause gas bubbles to move, expand, or collapse. At the cellular level, even slight movement of gas bubbles can potentially disrupt cellular connections.
Output display standard