Ultrasound biologic effects: a suggestion of strain specificity

Pregnant hybrid LAF1/J mice were exposed to continuous-wave ultrasonic energy at a frequency of 1 MHz at a spatial peak intensity of either 2.5 W/cm2 or O W/cm2 (sham) for 20 seconds on the eighth day of gestation. Fetal weight (day 18 of gestation) and postpartum pup weight (21, 29 and 42 days post conception) were determined. No significant differences in weight were observed. This result differs from findings in others studies using outbred mouse strains. It is suggested that hybrid mice exposed to ultrasonic energy in utero may be more resistant to alterations in fetal and pup weight progression as compared with outbred strains.