Routine ultrasound scanning in first trimester: what are the risks?

Acoustic exposure from modern ultrasonographic devices is capable of disturbing biological tissue to varying extent depending on the type of ultrasound examination and the particular tissue under investigation. There is no strong evidence that these biological effects present a serious health hazard, however, knowledge is incomplete, particularly from human studies. Although ultrasound induced heating can be significant in later pregnancy, it is unlikely that diagnostic ultrasound poses a significant thermal risk to the developing embryo when used according to published safety guidelines. Nevertheless, uncertainties remain, particularly for nonthermal effects in early pregnancy where shear stresses from radiation pressure may become an important factor. The likelihood of producing some biological effects can be enhanced by new procedures such as the use of gas encapsulated echo-contrast agents. The particular sensitivity of the embryo to physical damage together with uncertainties of both risk and benefit suggest that caution should be applied to the scanning of early first trimester uncomplicated pregnancy.