Dose-dependent effect of ultrasound on fetal weight in mice

Outbred non-Swiss albino mice (CF₁) were time-mated, exposed on the eighth day of gestation to 1 MHz continuous wave ultrasound, and examined on the eighteenth day of gestation. Seven exposure conditions (spatial average intensity versus exposure time) were employed for the 272 litters: 0 W/cm² (sham); 0.5 W/cm², 300 sec; 0.7 W/cm², 300 sec; 2.0 W/cm², 20 sec; 3.0 W/cm², 20 sec; 3.0 W/cm², 10 sec; and 5.5 W/cm², 10 sec. Relative to the sham group, every exposed group exhibited a reduced average fetal weight, ranging from 5.3 to 17.5 per cent, and the nonparametric Kruskal-Wallis one-way analysis of variance by ranks indicated that the average fetal weight varied significantly, at the 0.001 level, with exposure condition. In addition, a linear dose-effect dependence of exposure condition versus average fetal weight was observed, in which the dose parameter was defined as I²t, where I is the spatial average exposure intensity and t is the exposure time.