Effects of Ultrasound Exposure on Pregnancy: A Study in the Mouse

Absfmcf-Pregnant mice at eight days of gestation (dg) underwent unilateral uterine irradiation at free-field temporal average intensities two to three orders of magnitude greater than those typically used clinically. Pregnant mice at 6, 7, or 9 dg underwent pulse-mode bilateral uterine irradiation at a free-field intensity of 0.65 W cm-'. The selection of these intensities was based on preliminary findings that such levels were required to produce dose response data for production of significant fetal bioeffects, including anomalies for the specific experimental irradiation protocol involved. Use of a matrix array for ultrasonic beam placement allowed precise definition of the area to be exposed while avoiding maternal leg nerve and spinal cord damage. The beam diameter (2 or 4 mm) for both pulse and continuous wave (CW) irradiations covered an 8-day-old mouse fetus within the 2- or 4-mm diameter half-intensity points. This heam-to-body size ratio is equivalent to that of clinically used real-time scanners and a 12-week human fetus. The specific biological end points studied were maternal mortality, mean litter size, mean litter weight, and fetal anomalies. This report permits a comparison of pulse and CM' regimes with regard to the same biological and thermal end points.