Prudent Use and Safety of Diagnostic Ultrasound in Pregnancy

Based on the epidemiologic data available and on current knowledge of interactive mechanisms, there is insufficient justification to warrant conclusion of a causal relationship between diagnostic ultrasound and recognized adverse effects in humans. Some studies have reported effects of exposure to diagnostic ultrasound during pregnancy, such as low birth weight, delayed speech, dyslexia, and non–right-handedness. Other studies have not demonstrated such effects. The epidemiologic evidence is based primarily on exposure conditions before 1992, the year in which acoustic limits of ultrasound machines were substantially increased for fetal/obstetric applications. In addition, the absence of conclusive studies demonstrating causal relationships does not constitute proof that adverse effects are impossible. Therefore, prudent use and safety of diagnostic ultrasound in pregnancy should involve a conservative approach that obtains necessary diagnostic information at minimal exposure.

The American Institute of Ultrasound in Medicine (AIUM) advocates the responsible use of diagnostic ultrasound and strongly discourages the nonmedical use of ultrasound. The use of ultrasound without a medical indication to view the fetus, obtain images of the fetus, or identify the fetal external genitalia is inappropriate and contrary to responsible medical practice.

The AIUM recommends that appropriately trained and credentialed medical professionals who have received specialized training in fetal imaging perform all fetal ultrasound examinations. These individuals have been trained to recognize medically important image patterns, such as may be present with congenital anomalies, as well as artifacts associated with ultrasound scanning that may mimic pathology. Furthermore, they should be proficient in the use of techniques to avoid unnecessary ultrasound exposure to the fetus. The AIUM emphasizes that all imaging requires proper documentation and a final report for the patient medical record signed by a physician or  an advanced clinical provider legally responsible for interpretation.

Although the general use of ultrasound for medical diagnosis is considered safe, ultrasound energy has the potential to produce biological effects. It is the responsibility of the operator to minimize the possibility of ultrasound bioeffects by limiting exposure and dwell times, by monitoring the output display indices (thermal index [TI] and mechanical index [MI]), and by using Doppler and elasticity imaging and measurement appropriately only for a medical indication.

Fetal Heart Rate Evaluation

Although Doppler instruments without imaging capability are permissible to be used, spectral Doppler imaging should not be used to document the fetal heart rate unless clinically indicated. When attempting to document the fetal cardiac activity or obtain the heart rate with a diagnostic ultrasound system, the AIUM recommends using either an M-mode or a B-mode scan, keeping the TI as low as possible, preferably less than or equal to 0.7, and not prolonging the procedure beyond what is necessary to obtain the measurement.¹ Use the TI for soft tissues for the TI if pregnancy is less than 10 weeks; use the TI for bone if 10 or more weeks.

If an M-mode scan cannot be obtained at an embryonic size (crown-rump length) of 2 mm to 1 cm (approximately 5+ to 7 weeks), the heartbeat may be visualized by B-mode imaging and retained for documentation. Pulsed Doppler (spectral, power, and color flow imaging) ultrasound should not be used routinely due to increased acoustic output.

Doppler Ultrasound During 11- to 14-Week Scans (or Earlier in Pregnancy)

The use of Doppler ultrasound during the first trimester is currently being promoted as an aid for screening and diagnosis of some congenital abnormalities. The procedure requires considerable skill and subjects the fetus to extended periods of relatively high ultrasound exposure levels. Due to the increased acoustic output of spectral Doppler ultrasound, its use in the first trimester should be viewed with caution. Spectral Doppler imaging should only be used when there is a clear benefit/risk advantage and both the TI and examination duration are kept low. Protocols that typically involve TI values lower than 1.0 reflect minimal risk. Comparable to the World Federation for Ultrasound in Medicine and Biology/International Society of Ultrasound in Obstetrics and Gynecology statement, we recommend that²:

1. All scans should begin at a displayed TI of 0.7 because the total duration of an ultrasound examination during pregnancy cannot be known in advance. Higher outputs should be used only if needed to obtain adequate images and in accordance with the as low as reasonably achievable (ALARA) principle.³
2. Pulsed Doppler (spectral, power, and color flow imaging) ultrasound should not be used routinely.
3. Spectral Doppler ultrasound may be used for specific clinical indications, such as to refine risks for trisomies, and color Doppler imaging may be useful in an early anatomic evaluation of the fetus or placenta.
4. When performing a Doppler ultrasound examination, the displayed TI should be less than or equal to 0.7, provided adequate images can be obtained, and the exposure time should be kept as short as possible, consistent with acquisition of needed clinical information.
5. When using Doppler ultrasound for research, teaching, and training purposes, the displayed TI should be less than or equal to 0.7, and the exposure time should be kept as short as possible, consistent with the purposes of the scan. Informed consent should be obtained.
6. In educational settings, a discussion of first-trimester pulsed or color Doppler ultrasound should be accompanied by information on safety and bioeffects (eg, TI, exposure times, and how to reduce the output power).
7. When scanning maternal uterine arteries in the first trimester, there are unlikely to be any fetal safety implications as long as the embryo/fetus lies outside the Doppler ultrasound beam.

Keepsake Fetal Imaging

The AIUM encourages patients to make sure that practitioners using ultrasound have received formal education and training in fetal imaging to ensure the best possible results. 

The AIUM recognizes the growing pressures from patients for the performance of ultrasound examinations for bonding and reassurance purposes largely driven by advances in image quality of 3-dimensional (3D) sonography and by more widely available information about these advances. Although there is only some scientific evidence that 3D sonography has a positive impact on parental-fetal bonding, the AIUM recognizes that many parents may pursue scanning for this purpose. Such “keepsake imaging” currently occurs in a variety of settings, including the following:

1. Images or video clips given to parents during the course of a medically indicated ultrasound examination.
2. Images or clips given to volunteers who are scanned as part of diagnostic ultrasound education programs or demonstrations, provided that images are not used as an enticement to participate.
3. Freestanding commercial fetal imaging sites, usually without any physician review of acquired images and with no regulation of the training of the individuals obtaining the images; these sites are sometimes called “baby video studios,” and these videos are sometimes called “entertainment videos.”
4. As added-cost visits to a medical facility (office or hospital) outside the coverage of contractual arrangements between the provider and the patient’s insurance carrier. The AIUM believes that added-cost arrangements other than those for providing patients images or copies of their medical records at cost may violate the principles of medical ethics of the American Medical Association (AMA)^4–6 and the American College of Obstetricians and Gynecologists (ACOG).⁷

The AIUM, therefore, recommends that only scenarios 1 and 2 above are consistent with the ethical principles of the AIUM and those of the AMA and ACOG.

The market for keepsake images is driven in part by past medical approaches that have used medicolegal concerns as a reason not to provide images to patients. Sharing images with patients is unlikely to have a detrimental medicolegal impact. The AIUM encourages sharing images with patients as appropriate when medically indicated obstetric ultrasound examinations are performed.

References

1. American Institute of Ultrasound in Medicine. Recommended maximum scanning times for displayed thermal index (TI) values. American Institute of Ultrasound in Medicine website. Approved October 30, 2016.

2. World Federation for Ultrasound in Medicine and Biology. WFUMB/ISUOG policy statement on souvenir imaging of the fetus. World Federation for Ultrasound in Medicine and Biology website. https://wfumb.info/2019/04/15/echoes-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2/. Posted April 15, 2019.

3. American Institute of Ultrasound in Medicine. As low as reasonably achievable (ALARA) principle. American Institute of Ultrasound in Medicine website. Approved May 19, 2020.

4. American Medical Association. E-8.062: Sale of Non–Health-Related Goods From Physician’s Offices. Chicago, IL: American Medical Association; 1998.

5. American Medical Association. Addendum III: Council on Ethical and Judicial Affairs Clarification on Sale of Products from Physicians' Offices (E-8062 and E-8.063). Chicago, IL: American Medical Association; 2000.

6. American Medical Association. E-8.063: Sale of Health-Related Products From Physician’s Offices. Chicago, IL: American Medical Association; 1999.

7. American College of Obstetricians and Gynecologists. Commercial enterprises in medical practice: ACOG Committee Opinion No. 359. Obstet Gynecol 2007;109:243–245.