I have added several abstracts of papers here on this topic - descriptive blog post to follow
J Obstet Gynaecol Can. 2005 Jun;27(6):572-80.
Obstetric ultrasound biological effects and safety.
[Article in English, French]
Bly S, Van den Hof MC; Diagnostic Imaging Committee, Society of Obstetricians and Gynaecologists of Canada.
To review the biological effects and safety of obstetric ultrasound.
Outline the circumstances in which safety may be a concern with obstetric ultrasound.
Medline was searched, and a review of a document on this subject published by Health Canada and of bibliographies from identified articles was conducted.
Review by principal authors and the Diagnostic Imaging Committee of the SOGC. The level of evidence was judged as outlined by the Canadian Task Force on the Periodic Health Examination.
BENEFITS, HARMS, AND COSTS:
Obstetric ultrasound should only be done for medical reasons, and exposure should be kept as low as reasonably achievable (ALARA) because of the potential for tissue heating. Higher energy is of particular concern for pulsed Doppler, colour flow, first trimester ultrasound with a long transvesical path (> 5 cm), second or third trimester exams when bone is in the focal zone, as well as when scanning tissue with minimal perfusion (embryonic) or in patients who are febrile. Operators can minimize risk by limiting dwell time, limiting exposure to critical structures, and following equipment generated exposure information. Recommendations 1. Obstetric ultrasound should only be used when the potential medical benefit outweighs any theoretical or potential risk (II-2A). 2. Obstetric ultrasound should not be used for nonmedical reasons, such as sex determination, producing nonmedical photos or videos, or for commercial purposes ( III-B). 3. Ultrasound exposure should be as low as reasonably achievable (ALARA) because of the potential for tissue heating when the thermal index exceeds 1. Exposure can be reduced through the use of output control and (or) by reducing the amount of time the beam is focused on one place (dwell time) (II-1A). 4. All diagnostic ultrasound devices should comply with the output display standards (MI and TI) (III-B). 5. When ultrasound is done for research or teaching purposes, exposed individuals should be informed if either the MI or TI are greater than 1 and how this exposure compares to that found in normal diagnostic practice (III-B). 6. While imaging the fetus in the first trimester, Doppler and colour Doppler should be avoided (III-B).
Med Hypotheses. 2012 Apr;78(4):539-41. doi: 10.1016/j.mehy.2012.01.030. Epub 2012 Feb 10.
Long-term effects of in utero Doppler ultrasound scanning--a developmental programming perspective.
Aiken CE1, Lees CC.
Ultrasound scanning has been used as a diagnostic and screening tool in obstetric practice for over 50 years. There is no evidence of immediate or long-term harm to the developing fetus from exposure to B mode ultrasound. However, exposure to high levels of Doppler ultrasound during early development is increasingly common, and the full safety implications of this exposure are not clear. Doppler ultrasound exposure in utero gives rise to increased apoptosis in animal models, and there is evidence of the effects of exposure to Doppler ultrasound persisting throughout life, with increased non-right-handedness observed in human epidemiological studies. We consider the idea that there may be long-term developmental implications for fetuses exposed to Doppler ultrasound early in gestation. These effects may be mediated via thermal or mechanical disruption to the developing conceptus, giving rise to free radical damage. Excess free radical exposure early in gestation is a strong candidate for the final common pathway underlying developmental programming effects, and gives rise to concern that fetuses exposed to high levels of ultrasound are at risk of a developmental programming effect. It is suggested that there is a need for animal studies of developmental programming using exposure to Doppler ultrasound scanning as the exposure of interest, and for more observational data to be collected in the clinical setting. While these data are collected, it seems prudent to continue to adhere to the principle of 'as low as reasonably achievable' (ALARA) when exposing first-trimester fetuses to Doppler ultrasound.
Clin Obstet Gynecol. 2012 Mar;55(1):188-98. doi: 10.1097/GRF.0b013e3182488386.
A symposium on obstetrical ultrasound: is all this safe for the fetus?
Sheiner E1, Abramowicz JS.
Diagnostic ultrasound is a form of energy that has the potential for effects in tissues (bioeffects). The 2 most likely mechanisms are heating and cavitation. The thermal index (TI) expresses the potential for rise in temperature. The MI indicates the potential for the ultrasound to induce inertial cavitation. Scarce data exist regarding instrument's acoustic output for routine ultrasound examinations. Data collected during routine ultrasound examinations (first trimester for viability, nuchal translucency, anatomy surveys including 3-dimensional/4-dimensional studies and growth studies) show that "gray-scale" B-mode ultrasound is associated with a negligible rise in TI. However, Doppler studies show significantly higher levels of TI, which can reach 1.5 and above.
Ann Afr Med. 2012 Jan-Mar;11(1):1-4. doi: 10.4103/1596-3519.91006.
On the safety of diagnostic ultrasound in pregnancy: have we handled the available data correctly?
Bello SO1, Ekele BA.
Robust evidence of the bioeffects of ultrasound is available from animal studies but human studies are less convincing. Nevertheless, it is disturbing that the only response to safety issues is a twenty-year old principle known as ALARA (As Low As Reasonably Applicable). Using experience from obstetrics and toxicology, and drawing information mainly from two recent systematic reviews and meta-analysis that extensively covered the subject of ultrasound safety, this review captures the current knowledge of ultrasound bioeffects and suggests that it may be time for an international, multidisciplinary meeting on ultrasound safety to decide how to provide the evidence (available data) to patients and sonographers in a succinct manner.