The Effects of Prenatal Ultrasound Exposure on Postnatal Growth and Acquisition of Reflexes

Abstract

The examination of pregnant women using diagnostic ultrasound has increased greatly over past decades in the United States. As sonography techniques have been altered and refined, there has been renewed interest concerning possible effects on the developing fetus, since exposures in mid-gestation occur during the sensitive period of brain development. The present study is concerned with possible neonatal functional deficits due to exposure of the fetus to ultrasound. An ultrasound exposure tank was designed specifically for controlled studies of bioeffects. Thirty-six pregnant rats were anesthetized, immersed to the axilla in a water tank and exposed on the 15th, 17th and 19th days of gestation. Twelve rats were exposed to 5.0 MHz pulsed ultrasound of effective pulse duration equal to approximately 0.170 microseconds, pulse repetition rate 1 kHz, and a spatial peak, temporal peak intensity (ISPTP) of 500 W/cm2, representing a clinically relevant exposure level. The spatial peak, pulse average intensity (ISPPA), spatial peak temporal average intensity (ISPTA) and maximum intensity (Im) were determined to be 100 W/cm2, 24 mW/cm2 and 230 W/cm2, respectively. The maximum rarefaction pressure, pr, was measured as 12.5 x 10(5) Pa, and the total power was 2.5 mW. Twelve other rats were exposed to 1500 W/cm2, ISPTP (ISPPA, 350 W/cm2; ISPTA, 58 mW/cm2; Im, 600 W/cm2). Twelve additional rats were sham-exposed. Since the focal area was about 0.5 cm2, computer-controlled stepper motors moved the rats through the ultrasound field to assure uniform exposure of the abdominal/pelvic region. Total exposure time was 35 min. Additionally, a miniature thermocouple was implanted in a few rats to verify that no significant increase in body temperature took place during exposure. All neonates were subjected to five reflex tests and observed for four physiological parameters. Postnatal growth also was monitored. Analyses of the data indicate there were no significant alterations in neonatal development or postnatal growth due to exposure to 5.0 MHz ultrasound below an intensity (ISPTP) of 1500 W/cm2. Studies continue to be completed at higher exposure levels to determine the margin of safety, and the animals will continue to be monitored and evaluated through young adulthood to determine if there are long-term behavioral effects due to fetal exposure to ultrasound.

Effects of Prenatal Ultrasound Exposure on Adult Offspring Behavior in the Wistar Rat

“…Postnatal weights of female and male offspring were monitored weekly for 20 weeks and were published previously. There were no significant dose-related alterations in postnatal weight or postnatal growth rates (18). Adult behavioral tests were initiated on postnatal Day 60.…”

Gestational stage sensitivity to ultrasound effect on postnatal growth and development of mice

“…Experimental efforts to delineate the biological effects of ultrasound on in utero development have been inconclusive. Some studies have reported increased malformation rates (Stolzenberg et al, 1980a;Saravazayan et al, 1982;Takabayashi et al, 1985), while others have found no such effects (Kimmel et al, 1983(Kimmel et al, , 1989Gates, 1984, 1985;Child et al, 1984Child et al, , 1989Vorhees et al, 1991;Jensh et al, 1994). Furthermore, there are conflicting reports concerning the effects of ultrasound exposure on body weight and behavioral changes (Stewart et al, 1985;Hendrickx, 1989a, 1989b;Norton et al, 1991;Hande and Uma Devi, 1992, 1993Newnham et al, 1993;Vorhees et al, 1994;Uma Devi et al, 1995;Fisher et al, 1996;Suresh et al, 1996).…”