Routine fetal ultrasound screening is virtually ubiquitous in the U.S. and many other countries, where the majority of healthcare providers and expectant parents may assume that “the science is settled” regarding the safety of ultrasound scanning.
Many pregnant women receive as many as 17 or more scans over the course of their pregnancy. But in the field of medical ultrasound, where the technology was introduced so swiftly and has changed so drastically without exhaustive testing for safety and efficacy, can the science really be considered “settled?” Experts across multiple disciplines have consistently expressed concerns about safety, risks, and perceived benefits of fetal ultrasound.
Below is a brief explanation of ultrasound technology and a summary of possible risks associated with fetal ultrasound scanning. The second article in this series will examine potential benefits of ultrasound in special circumstances, and alternative methods which provide information traditionally obtained through routine ultrasound scans.
Every pregnant mother should be given adequate opportunity to review these risks and benefits carefully in the context of her own health and circumstances before she opts for or against one or more ultrasound scans during her pregnancy.
What Is Ultrasound?
Ultrasounds are sound waves occurring at frequencies outside the range of normal human hearing, at approximately 20 kilohertz (kHz) or higher. Fetal ultrasound devices use a transducer to convert energy into sound waves, which bounce off surfaces to create images of a growing fetus and/or detect the echo of a fetal heartbeat. Different ultrasound technologies employ waves of varying frequency (pitch) and intensity (volume). Intensity denotes the amount of energy colliding with the surfaces being observed, expressed in milliwatts per square centimeter (mW/ cm2).
Acoustic radiation does not directly cause mutagenic effects such as those associated with ionizing radiation, but ultrasound procedures produce three mechanical effects which may alter living tissue in a developing fetus: heat, cavitation, and acoustic streaming. These properties of ultrasound have been associated with potentially significant teratogenic effects, which will be examined further below. The frequency, as well as the intensity and duration of the sound waves in any given procedure, contribute to the strength of its effects on the target being observed.
What Are The Risks of Fetal Ultrasound?
Pregnancy Loss and Fetal Injury
Ultrasound has been associated with increased risk of miscarriage, particularly during the first ten weeks of gestation when the embryo cannot dissipate excess heat generated by ultrasound waves.
One study demonstrated brain damage and behavioral abnormalities in mice exposed to ultrasound in utero. Effects on the brain were also studied by Dr. Manuel Casanova, who found troubling correlations between ultrasound exposure and characteristics of autism. Other significant implications for possible brain injury are findings that associate ultrasound exposure with delayed speech as well as left-handedness. Another study found that ultrasound caused changes to DNA in animal cells.
And finally, one study attempting to demonstrate the safety of repeat ultrasound scanning instead found that multiple scans significantly increased the risk for intrauterine growth retardation (IUGR).
False Positive and Missed Diagnosis
Another risk of routine ultrasound scanning is that of false positive diagnoses of birth defects or medical problems, while in other cases, serious birth defects may go undetected. There are very few conditions which can be effectively treated in utero, so it’s not clear that even a correct diagnosis will be helpful – but false diagnoses can dramatically increase stress during pregnancy, as well as the risk of unnecessary interventions. For instance, one 2007 study found that markers for Downs Syndrome have been found to be incorrectly identified 7-10% of the time in first and second-trimester scans, leading to false positive diagnoses 5% of the time.
Other conditions, even if correctly identified, will likely resolve on their own or cannot be improved through prenatal intervention. For instance, placenta previa will resolve before term in the vast majority of cases.
The full extent and spectrum of risks associated with ultrasound procedures as they are currently performed cannot be accurately assessed because the technology has expanded so drastically since routine ultrasound became standard in obstetric care. Current equipment has never been extensively studied. A 2008 study notes that safety evaluations to date “were conducted with commercially available devices predating 1992, having outputs not exceeding a derated spatial-peak temporal-average intensity of 94 mW/cm2. Current limits in the United States allow 720 mW/cm2 for obstetric modes.”
Even more concerning, another 2008 study revealed that the majority of ultrasound technicians did not understand the basic parameters of their equipment, in particular how to identify standard measures of safety. So there is potential for up to a seven-fold increase in the intensity of patient exposure, while technicians may not understand how to correctly administer procedures in compliance with established safety standards.
The potential risks of fetal ultrasound scanning identified in peer-reviewed research to date are significant. Finding a healthcare provider who is aware of the risks – and in particular, working with fully qualified ultrasound technicians familiar with the parameters of the equipment in use – are essential to safety in prenatal care.
However, there are special circumstances in which the benefits of ultrasound may outweigh the risks, as well as long-standing and cutting-edge alternatives which provide much of the information traditionally sought via fetal ultrasound. Part II of this series will examine those in detail.
What Are Your Thoughts On Fetal Ultrasound?
So far I’ve been grateful that my OB/GYN office doesn’t do ultrasounds that often. I had one when I went to the ER with a threatened miscarriage, one a few days later just to be sure that it was still only threatened and that baby was still alive. I had a 20 week one recently and, now that I’ve just been tested for malaria (I still think the babymoon to Cambodia was worth it though!) will have one more at 28 weeks. Unless there’s something else troubling about my pregnancy I won’t have any more.
Then again, I was also pleasantly surprised that they’d let me check out a blood sugar monitor and record pre/post meals for a week instead of doing the Glucola test. I don’t really have an option of another clinic (military medicine + living overseas) so having this one turn out so well is really nice.
Thanks for reading! Sounds like you had a wonderful postpartum experience in Cambodia 🙂
If you ever feel unsure about an ultrasound, please know that you have the right to refuse or ask the referring care provider what he or she is looking for and what evidence demonstrates that the information will ultimately improve your outcome.
If you do opt to have an ultrasound scan, it’s never a bad idea to ask the ultrasound tech if he or she knows where the thermal index and mechanical index are located on the display, and check that they’re sure they can keep the procedure within current safety standards. It’s okay to get up and walk out or ask for another tech if you don’t feel confident.
Please look for part two of this series, and an upcoming article on gestational diabetes and the glucose tolerance test, coming later this month. Thanks again for reading and commenting!
I suppose that despite the fact that ultrasounds have risks, what it ultimately comes down to is whether or not the benefits outweigh those risks… and it would seem that most people would agree that indeed they do. However I think it would be good to inform expecting mothers of these risks, since it really does seem that most assume ultrasounds are perfectly safe. Let them know about the risks and allow them to make an informed decision. Knowledge is power! 🙂
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