Developmental exposure of mice to pulsed ultrasound

Exposure of pregnant mice on gestation day (gd) 8 to 1 MHz continuous-wave ultrasound (0, 0.05, 0.50, or 1.00 W/cm2) was reported previously to result in a slight (nonsignificant) increase in malformations. The present study was conducted in a similar fashion using pulsed ultrasound but was designed to maximize the likelihood of finding effects of gd 8 ultrasound exposure on prenatal development. Pregnant ICR mice (approximately 60 animals/group) were exposed on gd 8 to pulsed ultrasound with a center frequency of 1 MHz at levels of 0 (sham control), 0.05, 0.50, or 1.00 W/cm2 (spatial average, temporal average intensities; ISATA) with a spatial peak, pulse average intensity (ISPPA) of 90 W/cm2 and pulse duration of 6.5 microseconds. Anesthetized animals were placed in a degassed water bath (30 degrees C) and exposed for two 10 min intervals during which the beam was centered 1 cm on either side of the abdominal midline. On gd 17, dams were killed; the uterus and its contents were weighed and examined; and live fetuses were weighed and examined for external, visceral, and skeletal malformations. Although one female in the 0.50 W/cm2 group and seven animals in the 1.00 W/cm2 group died following exposure, no other significant change from controls was seen in any maternal or fetal parameter evaluated. Thus the results of this study indicate that there was no detectable effect on prenatal development of mice following exposure to ultrasound on gd 8 (a time of maximal sensitivity), even at exposure intensities that were lethal to some maternal animals.