Effects of prenatal ultrasound exposure on adult offspring behavior in the Wistar rat

How safe is it to use ultrasound in prenatal medicine? Facts and contradictions - Part 2 - Laboratory experiments regarding non-thermal effects and epidemiological studies

The first part of this CME article (issue 5/20) provided a detailed examination of the biophysical effects of ultrasound waves, the exposure values, and in particular the thermal effect. In vivo and in vitro measurements have shown that the temperature increase in tissue associated with B-mode ultrasound is far too low to pose a potential risk. Even experiments with exposure values in the range of pulsed Doppler have shown that temperature increases of over 1.5 °C can only occur in areas in direct contact with the probe, thus making a limited exposure time particularly in the case of transvaginal application advisable. The second part of this CME article describes various laboratory and animal experiments for evaluating non-thermal effects and also presents the most important epidemiological studies in the last 30 years in the form of an overview and review. In addition to direct insonation of isolated cells to examine possible mutagenic effects, the blood of patients exposed in vivo to ultrasound was also analyzed in multiple experiments. Reproducible chromosome aberrations could not be found in any of the studies. In contrast, many experiments on pregnant rodents showed some significant complications, such as abortion, deformities, and behavioral disorders. As in the case of thermal effects, the results of these experiments indicate the presence of an intensity- or pressure-dependent effect threshold. Numerous epidemiological studies examining possible short-term and long-term consequences after intrauterine ultrasound exposure are available with the most important studies being discussed in the following. In contrast to information presented incorrectly in the secondary literature and in the lay press, health problems could not be seen in the children observed in the postpartum period in any of these studies.

Severity of ASD symptoms and their correlation with the presence of copy number variations and exposure to first trimester ultrasound

Current research suggests that incidence and heterogeneity of autism spectrum disorder (ASD) symptoms may arise through a variety of exogenous and/or endogenous factors. While subject to routine clinical practice and generally considered safe, there exists speculation, though no human data, that diagnostic ultrasound may also contribute to ASD severity, supported by experimental evidence that exposure to ultrasound early in gestation could perturb brain development and alter behavior. Here we explored a modified triple hit hypothesis [Williams & Casanova, ] to assay for a possible relationship between the severity of ASD symptoms and (1) ultrasound exposure (2) during the first trimester of pregnancy in fetuses with a (3) genetic predisposition to ASD. We did so using retrospective analysis of data from the SSC (Simon's Simplex Collection) autism genetic repository funded by the Simons Foundation Autism Research Initiative. We found that male children with ASD, copy number variations (CNVs), and exposure to first trimester ultrasound had significantly decreased non-verbal IQ and increased repetitive behaviors relative to male children with ASD, with CNVs, and no ultrasound. These data suggest that heterogeneity in ASD symptoms may result, at least in part, from exposure to diagnostic ultrasound during early prenatal development of children with specific genetic vulnerabilities. These results also add weight to on-going concerns expressed by the FDA about non-medical use of diagnostic ultrasound during pregnancy. Autism Res 2017, 10: 472-484. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

Mice exposed to diagnostic ultrasound in utero are less social and more active in social situations relative to controls

Clinical use of diagnostic ultrasound imaging during pregnancy has a long history of safety and diagnostic utility, as supported by numerous human case reports and epidemiological studies. However, there exist in vivo studies linking large but clinically relevant doses of ultrasound applied to mouse fetuses in utero to altered learning, memory, and neuroanatomy of those mice. Also, there exists a well-documented significant increase in the likelihood of non-right-handedness in boys exposed to diagnostic ultrasound in utero, potentially relevant given the increased prevalence of autism in males, and reports of excess non-right-handedness in this population. Motivated by these observations, we applied 30 minutes of diagnostic ultrasound to pregnant mice at embryonic day 14.5 and assayed the social behavior of their male pups 3 weeks after their birth. The ultrasound-exposed pups were significantly (P < 0.01) less interested in social interaction than sham-exposed pups in a three-chamber sociability test. In addition, they demonstrated significantly (P < 0.05) more activity relative to the sham-exposed pups, but only in the presence of an unfamiliar mouse. These results suggest that fetal exposure to diagnostic ultrasound applied in utero can alter typical social behaviors in young mice that may be relevant for autism. There exist meaningful differences between the exposure of diagnostic ultrasound to mice versus humans that require further exploration before this work can usefully inform clinical practice. Future work should address these differences as well as clarify the extent, mechanisms, and functional effects of diagnostic ultrasound's interaction with the developing brain.

Saving lives and changing family histories: appropriate counseling of pregnant women and men and women of reproductive age, concerning the risk of diagnostic radiation exposures during and before pregnancy

Over the past 50 years, our laboratory has provided consultations dealing with the risks of various environmental toxicant exposures during pregnancy. These contacts were primarily by telephone or written communications. Since the year 2000, the primary source of consultations has been via the internet. In 2007, the pregnancy website of the Health Physics Society received 1,299,672 visits. The contacts who downloaded information totaled 620,035. After reading the website information, 1442 individuals who were still concerned contacted me directly. Unfortunately, we have learned that many physicians and other counselors are not prepared to counsel patients concerning radiation risks. Approximately, 8% of the website contacts, who had consulted a professional, were provided inaccurate information that could have resulted in an unnecessary interruption of a wanted pregnancy. Research from our and other investigators' laboratories has provided radiation risk data that are the basis for properly counseling contacts with radiation exposures. Mammalian animal research has been an important source of information that improves the quality and accuracy of estimating the reproductive and developmental risks of ionizing radiation in humans. What are the reproductive and developmental risks of in utero ionizing radiation exposure? 1. Birth defects, mental retardation, and other neurobehavioral effects, growth retardation, and embryonic death are deterministic effects (threshold effects). This indicates that these effects have a no adverse effect level (NOAEL). Almost all diagnostic radiological procedures provide exposures that are below the NOAEL for these developmental effects. 2. For the embryo to be deleteriously affected by ionizing radiation when the mother is exposed to a diagnostic study, the embryo has to be exposed above the NOAEL to increase the risk of deterministic effects. This rarely happens when the pregnant women have x-ray studies of the head, neck, chest or extremities. 3. During the preimplantation and preorganogenesis stages of embryonic development, the embryo is least likely to be malformed by the effects of ionizing radiation because the cells of the very young embryo are omnipotential and can replace adjacent cells that have been deleteriously affected. This early period of development has been designated as "the all-or-none period." 4. Protraction and fractionation of exposures of ionizing radiation to the embryo decrease the magnitude of the deleterious effects of deterministic effects. 5. The increased risk of cancer following high exposures to ionizing radiation exposure to adult populations has been demonstrated in the atomic bomb survivor population. Radiation-induced carcinogenesis is assumed to be a stochastic effect (nonthreshold effect) so that there is theoretically a risk at low exposures. Whereas there is no question that high exposures of ionizing radiation can increase the risk of cancer, the magnitude of the risk of cancer from embryonic exposures following diagnostic radiological procedures is very controversial. Recent publications and analyses indicate that the risk is lower for the irradiated embryo than the irradiated child, which surprised many scientists interested in this subject, and that there may be no increased carcinogenic risk from diagnostic radiological studies. Examples of appropriate and inappropriate counseling will be presented to demonstrate how counseling can save lives and change family histories. The reader is referred to the Health Physics Society website to obtain many examples of the answers to questions posed by women and men who have been exposed to radiation (www.hps.org). Then click on ATE (ask the expert).

Fetal thermal effects of diagnostic ultrasound

Processes that can produce a biological effect with some degree of heating (ie, about 1 degrees C above the physiologic temperature) act via a thermal mechanism. Investigations with laboratory animals have documented that pulsed ultrasound can produce elevations of temperature and damage in biological tissues in vivo, particularly in the presence of bone (intracranial temperature elevation). Acoustic outputs used to induce these adverse bioeffects are within the diagnostic range, although exposure times are usually considerably longer than in clinical practice. Conditions present in early pregnancy, such as lack of perfusion, may favor bioeffects. Thermally induced teratogenesis has been shown in many animal studies, as well as several controlled human studies; however, human studies have not shown a causal relationship between diagnostic ultrasound exposure during pregnancy and adverse biological effects to the fetus. All human epidemiologic studies, however, were conducted with commercially available devices predating 1992, that is, with acoustic outputs not exceeding a spatial-peak temporal-average intensity of 94 mW/cm2. Current limits in the United States allow a spatial-peak temporal-average intensity of 720 mW/cm2 for fetal applications. The synergistic effect of a raised body temperature (febrile status) and ultrasound insonation has not been examined in depth. Available evidence, experimental or epidemiologic, is insufficient to conclude that there is a causal relationship between obstetric diagnostic ultrasound exposure and obvious adverse thermal effects to the fetus. However, very subtle effects cannot be ruled out and indicate a need for further research, although research in humans may be extremely difficult to realize.

Long-term effects of diagnostic ultrasound during fetal period on postnatal development and adult behavior of mouse

Pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, intensity 65 mW, I(SPTP) = 1 W/cm(2), I(SATA) = 240 W/cm(2)) for 10, 20 and 30 minutes on day 14 of gestation. Sham exposed controls were maintained for comparison. Fifteen pregnant mice were exposed for each group. Exposed as well as control animals were left to complete gestation and parturition. Ultrasound induced changes in maternal vaginal temperature was recorded. The changes in the physiological reflexes and postnatal mortality up to 6 weeks of age were recorded. The litters were subjected to behavioral tests for locomotor activity, learning and memory at 4 month and 1 year of age. Neither the physiological reflexes nor the postnatal mortality was affected by ultrasound exposure. However, there was a noticeable impairment in both locomotor and learning behavior even after a 10 min exposure, which further increased with increases in exposure time. Thus the present study demonstrates the neurotoxicity of diagnostic ultrasound and the high susceptibility of early fetal brain to induction of lasting detrimental changes by ultrasound exposure.

Intrauterine effects of ultrasound: animal studies

During the past several decades, the use of ultrasound technology in the clinical setting has greatly increased. Because nearly every pregnant woman receives at least one sonographic procedure today, there has been developing concern about the safety of such procedures. Since ultrasound exposure can result in hyperthermia and other physiological effects, the determination of a threshold or no-effect exposure has become a high-priority goal. Animal research has been important to the study of the effects of various exposures at all stages of pregnancy, since the clinical use of ultrasonography can occur during the preimplantation, organogenic, and fetal stages. Animal experiments using various mammalian species have been able to determine no-effect exposure levels for embryonic loss, congenital malformations and neurobehavioral effects. The preponderance of evidence from these studies indicates that, in the absence of a thermal effect, ultrasonography represents no measurable risk when used at recommended intensity levels.

Behavioral effects of prenatal exposure to pulsed-wave ultrasound in unanesthetized rats

The present experiment examined the developmental neurotoxicity of pulsed-wave (pw) ultrasound in rats, using an exposure system designed to eliminate restraint or anesthesia from the exposure conditions. Pregnant Sprague-Dawley CD rats trained to remain immobile in a water-filled ultrasound exposure tank were scanned with 3-MHz pw ultrasound at spatial peak temporal average intensities (ISPTA) of 0, 2, 20, or 30 W/cm2 on embryonic days 4-20 for approximately 10 min/day. The data showed that such insonation produced no adverse effects on maternal weight gain or reproductive outcome, nor on the postnatal growth or survival of the offspring. No exposure-related alterations in behavioral development were observed in the offspring of rats scanned with pw ultrasound during gestation. In addition, there was no consistent evidence of an ultrasound-associated change in the adult offspring behaviors tested; i.e., no treatment effects were found on measures of locomotor activity, water maze learning, and acoustic startle reactivity. An effect on tactile startle was observed on some trials in the low exposure group male offspring, but this effect was neither dose dependent nor consistent with any other finding. Overall, these results indicate that the neurobehavioral development of rats was not altered by prenatal exposure to pw ultrasound at ISPTA levels of up to 30 W/cm2.