Development of a useful technique for analyzing behavioral teratologic data

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.

Postnatal neurophysiologic effects of prenatal X-irradiation

Histological and neurophysiological effects of in utero irradiation were examined following exposure of pregnant Wistar rat to 2.0 Gy X-irradiation or sham-irradiated on the 17th day of gestation. The 234 newborns were monitored for the age of appearance of four selected physiologic markers and the age of acquisition of five selected reflexes. Offspring were evaluated as young adults using selected behavioural tests. Postnatal growth was monitored weekly. Selected offspring were autopsied to determine the presence of morphologic central nervous system alterations. The results indicated that 2.0 Gy X-irradiation during the foetal period in rat gestation caused permanent alterations in the mature adult organism, which include non-recuperable growth retardation, morphologic changes in the brain such as microcephaly, abnormal cerebellar cortical cellular patterns, and alterations in the cell architecture of the hippocampus; diminished attainment of selected reflexes; alterations in the appearance of selected physiologic markers; and changes in adult test performance indicating significant hyperactivity among the irradiated offspring. Such exposure to X-irradiation during this period results in behavioural and morphologic alterations, which persist throughout life.

Effects of low level prenatal 60Co gamma-irradiation on postnatal growth and behavior in mice

Pregnant Kun Ming strain mice were exposed to a total dose of 0, 0.1, 0.2, or 0.4 Gy from 60Co gamma-rays from the 13th to the 18th days of gestation. An overall delay of the appearance of two physiologic markers (pinna detachment, eye opening) and the age of acquisition of four reflexes (surface righting, air righting, auditory startle, visual placing) was observed in offspring exposed to 0.2 or 0.4 Gy in utero. Postnatal growth retardation, shortened length of hanging time, inhibited exploratory activity in the hole board test (decreased number of head-dipping), and hyperactivity in the open field test (shortened latency to leave the center area and increased number of squares entered) were also found among the offspring exposed to 0.2 Gy or more in utero. The results indicate that 0.1-0.2 Gy may represent a threshold range in mice for certain physiologic and behavioral effects resulting from continuous exposure to 60Co gamma-rays on the 13th-18th days of gestation.

Medical sonography: reproductive effects and risks

While it is clear that the levels and types of medical sonography that have been used in the past have no measurable risks, it would be inaccurate to label the modality of ultrasound as totally safe regardless of exposure. Most agents have reproductive risks and even teratogenic risks if the exposure is raised sufficiently. Thus the prudent use of sonography means that clinicians and designers of equipment have to maintain exposures far below the risks that have been demonstrated in animal studies and from the knowledge obtained about the physical changes that can be produced in humans as the absorbed dose is elevated. The reproductive risks were evaluated using five criteria: 1) human epidemiology, 2) secular trend data, 3) animal experiments, 4) dose response relationships, and 5) biologic plausibility. The analysis reveals that the human epidemiology does not indicate that diagnostic ultrasound presents a measurable risk to the developing embryo or fetus. Animal studies also indicate that diagnostic levels of ultrasound are safe and do not elevate the fetal temperature into the region where deleterious embryonic and fetal effects will occur. Because higher exposures of ultrasound can elevate the temperature of the embryo, the use of diagnostic procedures and the design of sonographic equipment should take into consideration the hyperthermic potential of higher exposures of ultrasound and the hypothetical additional risk of performing sonography on pregnant patients who are febrile. It would appear that if the embryonic temperature never exceeds 39 degrees C, then there is no measurable risk. We suggest that sonography (the field) and sonogram (the procedure) are the most appropriate and least anxiety provoking terms.