Stage Dependence of Ultrasound-Induced Embryotoxicity in the Rat

Abstruct-Experiments were performed to determine if stage of gestation affected the response of the rat embryo to ultrasound exposure. Individual embryos were exposed to a focused beam of continuous wave, 0.8 MHz ultrasound at 9, 10, 12, or 15 days of gestation (dg). Survival, weight, and morphology were evaluated at 20 dg. Embryolethality was similar with 9, 10, and 12 dg exposures, but tended to be less following exposure at 15 dg. Overall malformation incidence did not differ with stage of gestation, but the anatomic sites and the nature of the malformations were markedly affected. Malformations of the heart and great vessels were primarily associated with exposure at 9 dg. Microphthalmia and anophthalmia resulted from exposure at 9 and 10 dg and retinal disorganization at 12 and 15 dg. Fusion defects of the vertebral column and limb defects progressively increased in frequency with exposure later in gestation. The nature of the lesions of the brain and the face was different after exposure at 9 or 10 dg than at 12 or 15 dg. It appears that the pattern of sensitivity with gestational age for malformation production by ultrasound is similar to that reported for ionizing radiation and for thermal insult.