Effects of frequent prenatal ultrasound exposure on rabbit foetal growth

Abstract

Given the advancement of the technology and the extensive use of ultrasound imaging in obstetric application, there may be an equivalent increase in the concerns pertaining to the potential biological consequences relative to the exposure. Thus, this research is designed to determine the effects arising from frequent prenatal ultrasound exposure on foetal development. This experimental study involved six pregnant rabbits, exposed to different number of ultrasound exposures at three stipulated gestational stages, early, mid, and late gestation. Exposures were performed daily for five days (protocol of five scans) and daily for two days (protocol of two scans). Ultrasound output parameters were kept constant (exposure duration = 10 minutes; frequency = 8.0 MHz; spatial-peak temporal-average intensity (ISPTA) = 0.056 W/cm2; acoustic output power = 0.06 W; mechanical index (MI) = 0.7). The measurements of foetal bi-parietal diameter (BPD), occipito-frontal diameter (OFD) and femur length (FL) were obtained 12 hours after the last exposure. The experiment was repeated with the same subjects for the next gestational stages. There were significant differences in foetal BPD between groups of different number of ultrasound exposures in early stage of pregnancy (p < 0.05), with a negative correlation (p = 0.02, rs = -0.84). Number of exposures was found highly related to foetal BPD in early pregnancy (p = 0.02, r² = 0.77). There were also significant differences in foetal OFD between groups of different number of ultrasound exposures in early stage of pregnancy (p < 0.05), with a negative correlation (p = 0.04, rs = -0.72). Number of exposures was found fairly related to foetal OFD in early pregnancy (p = 0.04, r² = 0.64). Foetal FL also reported significant differences between groups of different number of ultrasound exposures in mid stage of pregnancy (p < 0.05), with a negative correlation in both mid and late stages of pregnancy (p = 0.02, rs = -0.84; p = 0.00, rs = -0.96, respectively). Number of exposures was found highly related to foetal FL in both mid and late stages of pregnancy (p = 0.02, r² = 0.78; p = 0.01, r² = 0.83, respectively). Results suggested that the exposure to frequent prenatal ultrasound might be associated with the effects observed on foetal BPD, OFD and FL, which plausibly cause the incidence of intrauterine growth restriction (IUGR). Further investigation is needed to account for the underlying factors responsible for the observed changes.