Ultrasound has always been considered a safe screening technology for pregnant women. But new evidence coming out of China suggests we may need to think again
It's something every obstetrician needs to see and every mother-to-be wants to have: an image of the unborn child that shows in clear detail the baby's tiny hands, fingers and toes. For the doctor, it's much more than a happy photo opportunity; it is a chance to ensure the overall health of the fetus, including the proper functioning of internal organs and tissues.
Ultrasound uses sound waves, at a frequency thousands of times above levels considered harmful to our hearing, to develop an image of organs and blood vessels. Since the growing fetus doesn't develop ears until the 24th week or so, parents-to-be are assured that ultrasound waves are safe, and certainly far safer than x-rays, which use electromagnetic radiation.
That much may be so, but it doesn't make prenatal ultrasound screening entirely safe—and evidence that has only recently surfaced suggests it isn't.
Private correspondence between the UK Department of Health and AIMS, a pressure group for better maternity services, reveals that routine prenatal ultrasound screening had never been properly tested for its safety before it was rolled out across National Health Service (NHS) hospitals and clinics in 1978.
Just four years later, the health minister Dr Gerard Vaughan was writing that it was "no longer ethically possible" to run independent human trials as so many women had already been screened.
But human studies were being carried out in China—on fetuses that had been aborted as a result of the country's 'one family, one child' policy—and a cache of 50 papers uncovered by medical researcher Jim West shows that the enormous heat generated by ultrasound changes the brain structure of the baby.
Clues from China A healthy woman in the West will usually have two ultrasounds during a pregnancy, but it can be more if she has a health problem, such as high blood pressure or diabetes, or if the initial scans picked up an abnormality in the fetus.
But in China, with so many human research papers pointing to ultrasound's possible dangers, sonographers—the ultrasound technicians—are not advised to use the technology as a just-in-case screening, and certainly not during the first trimester when most women in the West are first screened.
Professor Ruo Feng from the Institute of Acoustics at Nanjing University recommends that ultrasound should be restricted to assessing known medical problems—and pregnancy isn't a 'medical problem'—and that commercial or educational fetal ultrasound imaging, where the mother-to-be wants a keepsake image, for instance, should be prohibited.
Even an ultrasound deemed necessary should use the smallest dose possible, Professor Feng claims, and this was something that the US Food and Drug Administration (FDA) once agreed with. In 1985, it issued guidance on the level of intensity of an ultrasound scan, and yet inexplicably increased that level by 15-fold just seven years later.
In 1982, the World Health Organization (WHO) was also sounding a cautionary note. It warned that ultrasound can create "powerful shockwaves far above the speed of sound" and "cavitational bubble collapse temperatures of thousands of degrees"—a biological phenomenon that happens when ultrasound waves cause liquids to vibrate.
But what was this doing to the baby? By 2002, FDA researchers were getting worried. While diagnostic ultrasound was, on the whole, safe, "there have been some reports that there may be a relation between prenatal ultrasound exposure and . . . growth restriction, delayed speech, dyslexia and non-right-handedness."1
This is because any sudden heating from ultrasound could affect the neurological function and structure of the fetus, as Chinese researchers had observed. With temperatures rising in the womb by as much as 10°F (5.6°C), these sudden temperature highs could "affect behavioral and cognitive function, such as memory and learning," say researchers from Monash University in Australia.
Even more worryingly, the researchers say, these effects were observed more than 25 years earlier, when ultrasounds were not as powerful.2
Hotting up This shouldn't be news. Ultrasound was developed as a therapy—not a diagnostic system—when researchers noted that the heat it generated affected animal tissue.
Entire schools of fish were destroyed when exposed to high-intensity ultrasound, experiments in the 1920s discovered. Ultrasound is also used industrially to disintegrate and blend materials and to weld steel.
And yet, by the mid-1960s, it started to be used to monitor the fetus. Most of the research into fetal ultrasound had been carried out in the former USSR and never translated. Before it was fully rolled out across the UK, the country's Medical Research Council had considered running an independent trial into any possible dangers of ultrasound but decided against it.
And by 1982, the technology was too well established, as Dr Vaughan revealed in his letter to AIMS. "The use of ultrasound techniques has become so widespread that a controlled trial along the lines originally proposed would no longer be ethically possible," he wrote.
Despite these concerns, the Royal College of Obstetrics did publish a review three years later that gave the technology a clean bill of health, but this was quickly dismissed by experts who denounced it as lacking the "rigor which normally would be expected of its scientific committee." In other words, it was bad science.3
Since then, numerous animal studies have warned that ultrasound could be affecting brain development, causing memory problems and antisocial behavior—but have been dismissed because the results wouldn't necessarily translate to people.
Medical researcher Jim West wasn't convinced. If any researcher had used a screening technique called electrophoresis, which uses electric currents to reveal any ultrasound damage to DNA, he would be a step closer to knowing whether it was harmful or not.
His line of enquiry eventually led him to China, where researchers routinely use electrophoresis. He discovered one Chinese paper that referenced others, and he was eventually able to uncover 50 human ultrasound studies. The studies, which involved 2,700 pregnant women who had agreed to have an abortion under China's child planning policies, covered 23 years up to 2011.
The first study, the one that led West to the others, discovered that DNA from aborted fetal tissue had been damaged after just 10 minutes of low-frequency ultrasound.4 Although the damage was seen only in aborted tissue, and so the effects this would have had on a developing child can't be known, West believes it could have led to childhood cancers like leukemia and neonatal jaundice.5
Although this is conjecture, it is astonishing that proper, independent studies—that track the health and development of screened and unscreened children—have not been carried out to find out for sure. Several arguments block these trials from happening: they would be unethical, and, in any event, ultrasound is safe—two views that create a vicious circle.
The prevailing opinion was stated by two researchers who surmised that "the relative safety of ultrasound has been well established based on its use over several decades. One could postulate that humans are resistant to ultrasound-related biologic effects."6
If we're sure ultrasound is safe, any harm to the developing child—whether it's autism, behavioral problems or development issues—must have a different cause. But we'll never find out if we don't look.
Don't ask us The US is the only country that sets official safe levels of ultrasound intensity—even though the FDA, which sets the guidelines, made it less safe when it increased the threshold 15-fold in 1992.
But whatever the threshold may be, a survey of doctors, midwives and sonographers—who carry out the ultrasound tests—discovered that only one-third even knew what those safe levels were. Even less than a third knew where to find the indices on the ultrasound equipment's screens, while just one in five, or 22 percent, knew how to adjust the energy output on the machine they were using every day.1
The sound and the story Ultrasound was developed in the 1920s and 1930s as a therapy to treat a range of conditions from Parkinson's to cancer.
William Fry at the University of Illinois was an early pioneer and used it to destroy part of the brain to alleviate Parkinson's disease, or so he thought. By the 1950s, it was being used to treat people with rheumatoid arthritis and Ménière's disease, which can cause hearing loss, dizziness and vertigo.
But some believed it was a cure-all for a wide range of problems, from gastric ulcers to eczema, asthma, urinary incontinence and hemorrhoids, although there was more wishful thinking than science to support the approach.
It was in the 1940s that ultrasound was first mooted as a diagnostic tool, and by 1958, researchers in Lund, Sweden, were investigating its use for monitoring early-stage pregnancy. It got an early green light for safety when researchers tested it on pregnant rats, who survived the experience unscathed.
Similar work was being carried out in Soviet Russia, and by the mid-1960s, there was a sudden explosion of ultrasound clinics being set up across the US, Europe and Japan. New scanners were developed to meet the demand, using the basic A-mode technology and the B-mode, which produces a clearer and brighter image.
In 1982, around the time when ultrasound was being adopted in pediatric clinics, the World Health Organization sounded a warning. Ultrasound, it said, can "create powerful shockwaves far above the speed of sound."
Diagnostic ultrasound produces sound wave pressure that is thousands of times that of the hearing pain threshold, and it's a technology employed not just for fetal screening but in industry.