Postpartum survival of mice exposed in utero to ultrasound.

We found no credible enhancement of neonatal mortality in mice exposed in utero on Day 8 of gestation to ultrasound at 0.44 W/cm2 (+/- 20%) spatial average intensity, 2 MHz, continuous wave, for 60--180 s in a 37 degrees C water bath. This result is compared with the adverse effect on neonatal survival reported by Curto [in Ultrasound in Medicine (Plenum, New York, 1976), Vol. 2, pp. 535--536] for exposure on Day 14 of gestation at about 0.125 to 0.5 W/cm2, 1MHz, continuous wave, for 180 s in a 30 degrees C bath. It is concluded that a temporary reduction in fetal viability, lasting from 4 days to less than 10 days after exposure, could account for both sets of data. It is also evident from these data that improved methods of determining intensities within mammalian tissues are highly desirable.