Medical sonography: reproductive effects and risks

Lauriston S. Taylor lecture: fifty years of scientific research: the importance of scholarship and the influence of politics and controversy

Over the past 50 years our laboratory has performed and published many studies in the fields of teratology, radiation biology and radiation embryology. The early work took place when I was a research employee at the University of Rochester Manhattan Project in 1944 and where I had my introduction to embryology and genetics. Over the years our lab has provided consultations dealing with the risks of various environmental toxicant exposures during pregnancy. With the advent of the Internet, consulting has become more rapid and efficient. In the past year our pregnancy Web site of the Health Physics Society received approximately 154,000 hits, of which over a thousand contacts were still quite anxious after reading the Web site answers and requested a personal consultation. From this extensive experience we have learned that many physicians and other counselors are not prepared to counsel patients concerning radiation risks. Approximately 8% of the patient contacts who have consulted a professional have been provided with inaccurate information that would have resulted in an unnecessary interruption of a wanted pregnancy. There are five areas of radiation embryology that are considered to be controversial. 1) Can the fetus be harmed by ionizing radiation if the fetus is not directly exposed? 2) Is the production of mental retardation from radiation during pregnancy a threshold phenomenon? 3) Does fractionation and protraction of radiation decrease the magnitude of the reproductive and developmental risks? 4) Is there a period during pregnancy when radiation will result in an increased mortality but not an increase in malformations? 5) How sensitive is the fetus to the oncogenic effects of radiation? We utilize the scientific information obtained from studies in these five areas to counsel patients concerning pregnancy radiation risks. The willingness and persistence of scientists to debate the controversial aspects of this research and apply the best available scientific information to assist patients in turmoil about the risks of radiation to themselves and their offspring has saved thousand of lives and changed family histories.

Effect of diagnostic ultrasound during the fetal period on learning and memory in mice

BACKGROUND

An experiment was conducted to find out whether in utero exposure to diagnostic ultrasound leads to changes in postnatal behavior in adult mice.

METHODS

A total of 15 pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, 65 mW/cm(2), intensity((spatial peak-temporal peak)) (I(SPTP))=1 mW/cm(2), intensity((spatial average-temporal average)) (I(SATA))=240 mW/cm(2)) for 30 min on day 14 or 16 of gestation. All exposed as well as control animals were left to complete gestation and parturition. Their offspring were used in our further studies. They were monitored during early postnatal life for standard developmental markers (such as pinna detachment, eye opening and fur development) and postnatal mortality was recorded up to 6 weeks of age. The litters were subjected to behavioral tests for learning and memory at 4 months of age. Representative animals from each group were sacrificed and the hippocampal region of the brain was assayed for biogenic amines, noradrenaline, dopamine, serotonin (5-HT) and 5-HT's metabolite, 5-hydroxy indoleacetic acid (5-HIAA), in order to determine whether ultrasound exposure produced any biochemical changes in the hippocampal region of the brain. Coronal sections from the dorsal hippocampus from the representative animals from each group were processed for staining and the number of neurons was counted.

RESULTS

Neither the standard developmental markers (such as pinna detachment, eye opening and fur development) nor the postnatal mortality was affected by ultrasound exposure. However, there was a significant impairment in learning (hole board test) and memory functions (shuttle box test) in both the exposure groups. Significant reductions in the biogenic amines and the decrease in the neuronal density were found only in day 14th pc ultrasound-exposed group compared with the control animals. The 16th day exposure group is relatively resistant to ultrasound-induced impairment of brain functions.

CONCLUSIONS

The results suggest that the early fetal brain is highly susceptible to induction of neurobehavioral changes by ultrasound exposure.

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

BACKGROUND

An experiment was conducted to find out whether ultrasound exposure leads to changes in postnatal growth and development in the mouse.

METHODS

A total of 15 pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, 65 mW/cm2, I(SPTP) = 1 mW/cm2 Intensity(Spatial Peak-Temporal Peak), I(SATA) = 240 mW/cm2 Intensity(Spatial Average-Temporal Average)) for 30 min for a single day between days 10 and 18 of gestation (GD 10-18). Virgin female mice were placed with same age group males for mating in the ratio 2 females : 1 male and examined the next morning for the presence of vaginal plug, a sign of successful copulation. The females with vaginal plugs were separated and labeled as 0-day pregnant. Maternal vaginal temperature was also measured. A sham exposed control group of 15 pregnant mice was maintained for comparison. All exposed as well as control animals were left to complete gestation and parturition. Their offspring were used in our further studies. They were monitored during early postnatal life for standard developmental markers, postnatal mortality, body weight, body length, head length, and head width, and growth restriction was recorded up to 6 weeks of age.

RESULTS

An exposure to ultrasound induced nonsignificant deviations in the maternal vaginal temperature or developmental markers. Significant low birth weight was observed in the present study, after exposure at GD 11, 12, 14, and 16. However, 14 and 16 days postcoitus during the fetal period appears to be the most sensitive to the ultrasound effect, in view of the number of different effects as well as severity of most of the observed effects when exposed on these gestation days.

CONCLUSIONS

The results indicate that diagnostic ultrasound can induce harmful effects on mouse growth and development when given at certain critical periods of gestation.

Nongenital malformations following exposure to progestational drugs: The last chapter of an erroneous allegation

In the late 1960s and 1970s, a number of epidemiological studies were published indicating that pregnant women who were exposed to an array of sex steroids delivered infants with an increased incidence of nongenital congenital malformations. Because of these publications, the Food and Drug Administration (FDA), in conjunction with various pharmaceutical companies, labeled the therapeutic exposure of progestational drugs and contraceptives in pregnant women as a risk factor for limb-reduction defects (LRDs) and congenital heart defects (CHDs). Subsequently there was a rapid decrease in the exposure of pregnant women to these drugs and the initiation of numerous lawsuits alleging that a particular progestational drug was responsible for a child's nongenital congenital malformation. Wilson and Brent (1981) published an article indicating that epidemiological and animal studies of these drugs, and basic science did not support the package insert's warnings. Many new and previous animal and epidemiological studies did not support the FDA box warning. In 1987 the FDA held a hearing in which the FDA, the Teratology Society, the Centers for Disease Control and Prevention, the American College of Obstetrics and Gynecology, and other organizations supported the position that progestational agents did not result in nongenital malformations. An editorial appeared in Teratology congratulating the FDA for removing the warning label on oral contraceptives regarding nongenital malformations. In 1999 the FDA published new wording for package inserts that removed warnings for nongenital malformations for all progestational agents. In spite of the recent changes in the package inserts, lawsuits have alleged that progestational drugs cause nongenital malformations. It took 22 years from the time a box warning was required by the FDA until the warnings were removed in 1999. The 1999 FDA publication, which is a scholarly and objective document, should put an end to 2 decades of concern and anxiety for pregnant women or women of reproductive age. Could scientists, the pharmaceutical companies, or the FDA have prevented the mislabeling of progestational drugs with regard to their teratogenic risks? Was the epidemiological or teratology community at fault because they did not critique and respond to the early publications? Did the FDA act too slowly? The epidemiologic analyses, animal studies, and basic science principles have been reviewed, and it is obvious that clinically utilized progestational drugs do not cause nongenital malformations (i.e., LRDs and CHDs).

O conhecimento científico e tecnológico como evidência para políticas e atividades regulatórias em saúde

Nas últimas décadas, têm-se observado mudanças na organização do modelo ocidental de Estado, com clara tendência de redução das suas atividades econômicas e sociais diretas. Ao mesmo tempo, percebe-se a ampliação de alguns dos seus papéis na elaboração de políticas e como regulador de uma série de parâmetros da vida social. Nesse contexto, consolida-se a noção de que são cada vez mais necessários conhecimentos científicos que fundamentem os processos de tomada de decisões. A idéia de política baseada em evidência foi apropriada pelo Estado moderno, e na saúde vem recebendo especial atenção. Avalia-se que, assim procedendo, se ampliam as chances de se tomar decisões mais efetivas, trazendo maiores benefícios à saúde da população, com menos custos econômicos ou sociais. Essa nova abordagem torna o Estado um crescente consumidor dos resultados da atividade científica. O objetivo deste ensaio é discutir alguns aspectos da relação entre o processo de produção do conhecimento científico e os processos gerais de tomada de decisões na área da saúde, com maior ênfase naqueles relacionados às atividades regulatórias. Após rever a literatura recente sobre o tema, comenta-se a importância dessa discussão no contexto do SUS no Brasil.

Routine screening for fetal anomalies: expectations

Ultrasound has become a routine part of prenatal care. Despite this, the sensitivity and specificity of the procedure is unclear to many patients and healthcare providers. In a small study from Canada, 54.9% of women reported that they had received no information about ultrasound before their examination. In addition, 37.2% of women indicated that they were unaware of any fetal problems that ultrasound could not detect. Most centers that perform ultrasound do not have their own statistics regarding sensitivity and specificity; it is necessary to rely on large collaborative studies. Unfortunately, wide variations exist in these studies with detection rates for fetal anomalies between 13.3% and 82.4%. The Eurofetus study is the largest prospective study performed to date and because of the time and expense involved in this type of study, a similar study is not likely to be repeated. The overall fetal detection rate for anomalous fetuses was 64.1%. It is important to note that in this study, ultrasounds were performed in tertiary centers with significant experience in detecting fetal malformations. The RADIUS study also demonstrated a significantly improved detection rate of anomalies before 24 weeks in tertiary versus community centers (35% versus 13%). Two concepts seem to emerge from reviewing these data. First, patients must be made aware of the limitations of ultrasound in detecting fetal anomalies. This information is critical to allow them to make informed decisions whether to undergo ultrasound examination and to prepare them for potential outcomes.Second, to achieve the detection rates reported in the Eurofetus study, ultrasound examination must be performed in centers that have extensive experience in the detection of fetal anomalies.

Women's knowledge of prenatal ultrasound and informed choice

This study evaluated women's understanding of prenatal ultrasound in terms of meeting the requirements for informed choice. A cross-sectional survey was conducted to evaluate (1) how information is provided, (2) women's perceived value of the information received and, (3) their understanding of ultrasound in relation to the principles of informed choice. Women (n=113) completed a questionnaire prior to their 18-week ultrasound. Fifty-five percent stated they received no information from their care provider. Only 31.9% considered health care providers as a "very helpful" source of information. Yet, 69.0% stated their care provider gave them information that facilitated their understanding. Gaps were identified in women's understanding of ultrasound. Specifically, 46.0% did not view ultrasound as a screen for anomalies; some were uncertain about their safety (18.6%), diagnostic capabilities (26.5%), and limitations of testing (37.2%). These results suggest that women's understanding of ultrasound does not meet the requirements of informed choice.

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: human epidemiology

Ultrasound imaging has been used clinically as an effective diagnostic tool over the past 30 years. In spite of literally millions of examinations, there is no verified documented evidence of adverse effects in patients caused by exposure to diagnostic ultrasound. A number of epidemiological studies of intrauterine ultrasound exposure have been conducted, including several case-control and prospective randomized control studies. In some studies, an association of one or another bioeffect was identified, such as low birth weight, delayed speech, or increased incidence of left-handedness. However, with the exception of low birth weight, these findings have never been duplicated, and the great majority of such studies have been completely negative.

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.

Utilization of developmental basic science principles in the evaluation of reproductive risks from pre- and postconception environmental radiation exposures

The subject of the reproductive toxicity of various forms of radiation can be anxiety provoking to the public on two accounts, since reproductive failure engenders an unusual level of guilt and anger in the affected families, and radiation effects are misunderstood and feared by the public. Reproductive problems include an array of genetic and acquired diseases affecting parents and their offspring. Many of these problems are associated with the risk of being induced by preconception and/or postconception exposures to environmental agents. For the various forms of radiation, namely, ionizing radiation, ultrasound, low-frequency electromagnetic fields (EMF), and microwaves, the potential for producing reproductive effects varies considerably with the form of "radiation" and, of course, the dose. Whether the exposure occurs preconceptionally or postconceptionally is another major consideration. In evaluating the actual reproductive risks, we rely on accurate dosimetry and information obtained in epidemiological studies and animal studies. Epidemiological studies must demonstrate consistency of the reproductive finding, and animal studies should be designed to add to the findings of the epidemiological studies. Most importantly, the conclusions must not contradict the basic principles of teratology, genetics, and reproductive biology, and they should be biologically plausible. But frequently important basic science principles are ignored in the evaluation process. Yet developmental basic science principles can be instrumental in refuting or supporting the concern about possible risks. Although there is some overlap with regard to the preconception and intrauterine effects of ionizing radiation, there are significant differences. Preconception effects are mainly stochastic effects, while intrauterine effects are mainly deterministic effects. The stochastic genetic risks are lower than the deterministic risks at equivalent exposures. Thus, it is frequently difficult to demonstrate the occurrence of stochastic effects in populations that have received low preconception exposures to ionizing radiation. The reproductive effects from preconception and intrauterine exposures to electromagnetic fields (low-frequency EMF, video display terminals, microwaves) and ultrasound represent much different problems, since the main effects of microwaves and ultrasound occur because of their hyperthermic effects at high exposures. Low-frequency EMF does not have the capacity to produce hyperthermia, and none of these forms of nonionizing radiation has the specificity to damage the DNA comparable to the specificity of ionizing radiation. Not only do they not have targeted mutagenic effects at the usual exposures that populations receive, they are not cytotoxic at these exposure levels as well. From the viewpoint of biological plausibility, these other forms of radiation are much less likely to have the potential for producing reproductive toxicity at the usual population exposures.

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.

Bendectin: review of the medical literature of a comprehensively studied human nonteratogen and the most prevalent tortogen-litigen

OBJECTIVE

to review the extensive literature pertaining to the reproductive and teratogenic effects of Bendectin and the opinions of the scientific experts for the defense and plaintiff. These data were evaluated with regard to the reproductive risks of Bendectin providing a scientific framework for evaluating the views of the experts in the Bendectin litigation.

DESIGN

the Bendectin literature was primarily obtained from articles cited in Research Alert of the Institute for Science Information. Other articles were obtained from Medline, review articles, and colleagues. An attempt was made to be all-inclusive, citing and reviewing all articles related to each subject being discussed. The literature includes epidemiologic studies, animal studies, in vitro studies, and basic science articles related to the principles of teratology and reproductive toxicology. Review articles, meta analyses, editorials, commentaries, articles in the press, and case reports were also included.

METHODOLOGY

the methodology utilized for the evaluation of Bendectin teratogenicity was presented. It consists of a five-part analysis of epidemiologic studies, secular trend analysis, animal studies, dose-response relationships, and biologic plausibility.

CONCLUSION

the five-part analysis of Bendectin reproductive effects indicates that therapeutic use of Bendectin has no measurable teratogenic effects. Presentations by many of the plantiff's experts failed to meet the scientific standards that should be expected of knowledgeable scientists and contributed to the persistence of Bendectin litigation.

Teratogenic effects of repeated exposures to X-rays and/or ultrasound in mice

Pregnant Swiss mice were exposed to 9 mGy of 70 kVp X-rays or 10 min of ultrasound (3.5 MHz, approximately 65 mW, ISPTP = 1 W/cm2, ISATA = 240 mW/cm2) on Days 6.5 and 11.5 of gestation in four combinations: X-rays on both days (X + X), ultrasound on both days (U + U), X-rays on Day 6.5 postcoitus (PC) and ultrasound on day 11.5 PC(X + U) and ultrasound at 6.5 days PC and X-rays on day 11.5 PC(U + X). Sham-treated controls were maintained for comparison. Effects on prenatal development, postnatal growth and adult behavior were studied. U + U group showed an increase in percent growth retarded fetuses and a nonsignificant increase was seen in the U + X group. Transient growth retardation was observed in all the exposure groups. This is less likely to be of any biological significance as the animals recovered during postweaning period. The postnatal mortality was significantly higher only in the U + U group. In the X + U group, the exploratory activity was affected at 6 months of age. There was a significant change in the locomotor activity with a reduction in the total activity as 3 and 6 months of age in the U + U group. Latency in learning capacity was also noticed in this group. The results indicate that repeated exposures to ultrasound or its combination with X-rays could be detrimental to the embryonic development and can impair adult brain function when administered at certain stages of organogenesis.

Effect of ultrasound on DNA synthesis in tumor cells

The objective of this study was to consider the influence of continuous-wave (CW) ultrasound (800 kHz) on DNA synthesis in Ehrlich ascitic tumor cells in vitro. The 10-min irradiation was carried out in rotating polyethylene tubes (5 rpm). Incorporation of 3H-thymidine was employed to detect DNA synthesis. Replication and unscheduled (repair) DNA synthesis were distinguished by means of hydroxyurea treatment before insonation. It was established that the use of 0.5 W/cm2 and 1.0 W/cm2 (ISA) CW ultrasound interfered with DNA synthesis showing up as inhibition. The inhibition became most noticeable when starting insonation in a sample cooled to 5 degrees C. During insonation, the sample temperature was allowed to increase to the ambient (water bath) temperature of 37 degrees C. However, at an ultrasound intensity (SA) of 0.1 W/cm2 such inhibition was not proven, but a moderate stimulation of DNA synthesis was demonstrated. Changes in DNA synthesis after insonation were found to be transient because of a lack of stimulatory and/or inhibitory ultrasound effects after 1-h incubation at 37 degrees C. In our experimental conditions no effects on DNA synthesis due to the effects of the insonated medium on the cells were discernible. No statistically significant changes in unscheduled DNA synthesis were observed. Possible action mechanisms are discussed.

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

While there are no known risks associated with diagnostic ultrasound, uncertainty about the safety of prenatal ultrasound exposure remains. The purpose of the present experiment was to evaluate the behavioral teratogenic potential of continuous-wave (cw) ultrasound in rats, in the absence of maternal anesthesia or restraint. Pregnant CD rats, trained to remain immobile in a water-filled ultrasound exposure tank, were scanned with 3 MHz cw ultrasound at levels of 0, 2, 10, 20, or 30 W/cm2 ISPTA (spatial peak, temporal average intensity) on gestational days 4-20 for approximately 10 min/day. Offspring were examined postnatally for survival, growth, physical landmarks of development, behavioral development, and the adult functions of locomotor activity, learning and memory, and startle reactivity. No effects of prenatal ultrasound were found on maternal characteristics, offspring survival or growth, physical or behavioral landmarks of development, or adult tests of passive avoidance or startle. Effects at the highest intensity were obtained on corner and side locomotor activity and in a multiple-T water maze on measures of errors of commission and time spent finding the goal. The results showed that prenatal cw ultrasound in rats can induce effects on some postnatal neurobehavioral functions at high exposure intensities (30 W/cm2), but at lower intensities (2-20 W/cm2) no consistent evidence of neurobehavioral effects was observed.

Teratologic evaluation of rats prenatally exposed to pulsed-wave ultrasound

While there are no known risks associated with diagnostic ultrasound, uncertainty about the safety of prenatal ultrasound exposure remains. The purpose of the present experiment was to evaluate the teratogenic potential of pulsed-wave (pw) ultrasound in rats, in the absence of maternal anesthesia or restraint. Pregnant CD rats, trained to remain immobile in a water-filled ultrasound exposure tank, were scanned with 3-MHz pw ultrasound at levels of 0, 2, 20 or 30 W/cm2 ISPTA (spatial peak, temporal average intensity) on gestational days 4-19 for approximately 10 min/day. Examination of fetuses on E20 revealed no increase in skeletal or visceral malformations in groups exposed to pw ultrasound in utero. The number of implantations/dam was significantly increased in all pw ultrasound exposure groups compared to sham-exposed animals and, in a possibly related finding, resorptions were increased in the two highest exposure groups. Although significantly increased compared to controls, resorption frequencies in these groups were low (< 10%). No exposure-related changes in fetal weights were observed in offspring of rats scanned with pw ultrasound during gestation. The results indicate that, under the conditions described, no overt embryotoxicity is associated with gestational exposure to pw ultrasound intensities of up to 30 W/cm2.

Effect of in utero exposure to diagnostic ultrasound on the postnatal survival and growth of mouse

Pregnant Swiss albino mice were exposed to 3.5 MHz diagnostic ultrasound for 10 min (upper limit for ISPTP = 1 W/cm2 and for ISATA = 240 mW/cm2, acoustic power = approximately 65 mW) on day 3.5 (preimplantation period), 6.5 (early organogenesis period), 11.5 (late organogenesis period), or 14.5 (early fetal period) of gestation. The offspring were observed for changes in litter size at birth, and sex ratio at 4 weeks of age, and postnatal mortality and growth retardation up to 6 weeks of age. No significant difference from control in litter size or sex ratio was observed in the offspring exposed to ultrasound on any of the gestation days studied. Exposure at the early organogenesis period produced a marginally significant increase in the postnatal mortality. A significant number of ultrasound exposed animals showed lesser body weights than the control group. However this growth retardation was transient and the normal growth pattern was restored by 6 weeks of age. It is concluded that the early stages in mouse gestation may be sensitive to the lethal effects of ultrasound than the later stages of pregnancy. Even though a small increase in the postnatal mortality was observed in the ultrasound exposed animals, the normal growth was not affected in the surviving animals except for a transient growth retardation. Low birth weight may be a characteristic effect of exposure only at the preimplantation period.

Effect of prenatal ultrasound exposure on adult behavior in mice

Pregnant Swiss mice were exposed to diagnostic levels of ultrasound (3.5 MHz, Maximum acoustic output: ISPTP = 1 W/cm2 and ISATA = 240 mW/cm2, acoustic power = 65 mW) for 10 min on days 11.5 or 14.5 postcoitus (PC). At 3 and 6 months postpartum, offspring were subjected to the following behavioral tests: bright and dark arena test for locomotor/exploratory activity and passive avoidance test for learning and memory. Anxiolytic activity and latency in learning were noticed in the ultrasound-treated animals. The effect was more pronounced in the 14.5 days PC group than in the 11.5 days PC group. But memory was not affected in the ultrasound-exposed animals. There was a nonsignificant decrease in the total locomotor activity at 6 months of age in all the exposed animals. Thus, the present data demonstrate that exposure to diagnostic ultrasound during late organogenesis period or early fetal period in mice may cause changes in postnatal behavior as evidence by selected adult offspring behavioral tests. However, any conclusive statement in this regard should await results from more detailed investigations.

Evaluation of the bioeffects of prenatal ultrasound exposure in the cynomolgus macaque (Macaca fascicularis): III. Developmental and hematologic studies

The multiple applications of diagnostic ultrasound in obstetrics have resulted in a continued rise in the prenatal population exposed each year. Although human epidemiologic and experimental studies with various animal models have not consistently documented any significant, reproducible findings related to clinically relevant exposures, technologic changes in scanning equipment and gaps in our knowledge regarding the interaction(s) of ultrasound with tissues emphasize the need to pursue safety issues. Studies with nonhuman primates have provided information on the potential for pre and postnatal effects on offspring exposed repeatedly during gestation (ATL MK 600, 7.5 MHz, ISPTA = 27 mW/cm2; ISPPA = 85 W/cm2; Estimated power = 12 mW--scanned for 10 min 5 times weekly gestational day [GD] 20-35; 3 times weekly GD 36-60; once weekly for 20 min GD 60-150). These studies have indicated transient effects on body weight, white blood cell counts (WBCs), and muscle tone postnatally. In an effort to confirm these findings and focus on hematologic changes, a second series of studies was initiated using the same exposure conditions (N = 22; 11 exposed, 11 sham controls). Data derived from both studies were combined and confirmed transient reductions in body weights for infants up through 4 months of age (P < or = 0.03); no statistically significant differences in muscle tone were noted. Similar to the original findings, WBCs were transiently reduced on days 3 (P < or = 0.02) and 21 (P < or = 0.05); prenatal sampling indicated a significant difference between the groups on GD 140 (P < or = 0.04). No direct effects were evident in bone marrow aspirates collected on postnatal days 3, 9, and 21 +/- 1. Although animals were able to compensate for these observed changes and remained unaffected by their occurrence, additional studies will be required to further our understanding of this phenomenon.

Estimation of in situ ultrasound exposure during obstetric examinations

Layered tissue models are developed to estimate in situ ultrasound intensity during common obstetric examinations by incorporation of measured overlying tissue thicknesses with data on the attenuation properties of tissues. Results are compared with attenuation models recommended by the United States Food and Drug Administration (FDA) and National Council on Radiation Protection and Measurements (NCRP). For abdominal and transvaginal scanning in the first trimester, fixed attenuation models based on attenuation values of 1.2 dB/MHz and 0.6 dB/MHz, respectively, are representative of worst-case exposure conditions. For second and third trimesters, a fixed attenuation value of 0.8 dB/MHz is representative of worst-case exposure conditions. A fixed attenuation value of 1.0 dB/MHz is suggested for common Doppler examinations. The study suggests that the FDA-derating factor of 0.3 dB/cm.MHz may not give a conservative estimate of in situ intensity for certain obstetric examinations.