The Potential Risks of Fetal Ultrasound Frequencies

The Potential Risks of Fetal Ultrasound Frequencies

One frequency exposure source we don’t often consider is diagnostic ultrasonography, and specifically ultrasound procedures used during pregnancy and labor. Ultrasound is considered to be one of the most common routine prenatal care procedures, and has increased in frequency of use as well as intensity over the past decades, many women having ultrasounds performed several times throughout the duration of pregnancy. Another exposure source is continuous electronic fetal monitoring using Doppler ultrasound, which has become increasingly routine even in low-risk pregnancies, to monitor the fetal heartbeat and uterine contractions during labor.

Although fetal ultrasound is widely thought to be “safe and effective”, how much has this common procedure actually been studied, and are there any potential risks to the baby in utero during this delicate developmental stage?

The first thing to understand about ultrasound is that it utilizes high-frequency waves, but that these frequencies are not electromagnetic in nature.  They are a type of sound wave, or mechanical vibration, which moves in a purely longitudinal orientation.  They are not electromagnetic waves like electricity, cell phones and Wifi, and they are not a type of ionizing radiation like x-rays.  However, they still have a considerable effect on the body through thermal and mechanical means.

The “ultra” in ultrasound refers to frequencies above the range of human hearing, around 20,000 hertz (or 20 kilohertz) and higher.  In contrast, infrasound frequencies vibrate below the range of human hearing, and occur from natural phenomena like earthquakes, ocean waves and volcanic eruptions, as well as long-distance communication used by animals like whales and elephants.  Audible sound is the range between infrasound and ultrasound, and refers to sound waves that vibrate between 20 and 20,000 hertz, the frequency range that can be heard by the average human ear.

Sound waves always propagate through a medium, such as air, water or solid objects, causing the particles of the medium to vibrate.  The vibrations cause alternating regions of compression (where particles are closer together) and rarefaction (where particles are further apart).  This longitudinal disturbance of the medium creates friction that our ears can perceive within a certain range.  Outside of the range of hearing, the disturbance still creates friction, but we cannot perceive it audibly.

The way that ultrasound technology works begins with a transducer containing piezoelectric crystals, which generates high-frequency sound waves when an electric current is applied to the crystals.  The transducer is placed on the skin, in this case on the belly of a pregnant woman, and the ultrasonic waves penetrate the body, bouncing off tissues of varying densities inside, creating echoes.  The different ways that the waves bounce off tissues of greater and lesser density, including bone, skin, muscle, blood and other fluids, is then converted into digital data that is then used to produce an image of the inside of the body.

This image is called a sonogram, which loosely translates to “sound writing”, since the sound waves basically “write” the image that’s produced. In the image below you can see the sound waves at the bottom of the sonogram, and the image that it is "writing" above it.


Pregnant woman may undergo ultrasound procedures to generate sonograms of the growing fetus, usually for precautionary medical reasons, to assess the baby’s development and health.

Fetal ultrasound utilizes frequencies between 2 and 18 megahertz (MHz), equivalent to 2,000,000 to 18,000,000 hertz.  Although these are mechanical waves and not electromagnetic waves, the oscillations move at about the same speed as Wifi signals and 5G wireless technology.

Since ultrasounds do not directly expose the body to electromagnetic radiation, are usually non-invasive, and are generally comfortable for the mother, they have been widely thought to be a safe procedure.

However, there are issues with the available body of research on fetal ultrasounds that are worth examining.


Studies caution excessive or unnecessary fetal ultrasound use due to potential & unknown harms

A systematic study done by the World Health Organization in 2009 examined 61 publications reporting data from 41 different studies on fetal ultrasound use.  Although most of the studies appeared to conclude that ultrasound procedures during pregnancy are likely harmless, several warnings are noted at the end of the study review.

One limitation is that none of the analyzed studies had the objective of assessing potential adverse biological effects.  Ultrasound procedures were introduced in the 1970s, and the study review states that very little research has been done on possible adverse effects in humans.  It’s often the case with studies that if you aren’t looking for something, you won’t find it.

Also, around 90% of the included studies did not record the intensity or duration of exposure.  When assessing any exposure source for potential harm, the dose-response gradient is critically important.  Participants in many of these studies only received one or two ultrasounds, which is very low compared to common obstetric practices today.  If ultrasound exposure were to have a cumulative effect similar to radiation exposure, recording the intensity and duration is completely necessary to assess potential harm.

Another major limitation of this review is the studies mostly included exposures from before 1995, when the acoustic potency of the machines was much lower.  Modern ultrasound equipment has advanced considerably, and due to the lack of exposure regulations, current equipment can be eight times more powerful than the machines studied in the ‘90s, although they are used in the same way. Therefore, studies from this time period cannot automatically apply to modern day use.

The absence of studies geared toward the safety of fetal ultrasound use, combined with the wide availability of ultrasound equipment, has created a potentially dangerous situation.  Fetal ultrasound scans are widely prescribed by doctors, and requested by mothers, even for non-medical purposes (such as for “keepsake” photos).  This directly contradicts the cautionary advice of the Association for Medical Ultrasound, which “advocates the responsible use of diagnostic ultrasound and strongly discourages the nonmedical use of ultrasound.”  The Association cites a few studies that recorded harmful effects from pregnancy ultrasound exposure, including low birth weight, delayed speech and dyslexia, and states that there is not enough research to say for sure that it’s safe.  They go on to list very specific protocols that medical professionals should follow to ensure minimal harm.

The WHO study analysis states:

“There is a clear need for adequately designed large studies to investigate the safety of ultrasound scans performed with the newer equipment currently in use. However, because prenatal ultrasound is now commonplace, it may be difficult to perform randomized controlled trials without significant crossover. Particularly in developed countries, it would be difficult to recruit women willing to be randomized to a possible non-exposed control group.”

This is a good point, and is one reason why it would have been ideal for the studies to be done several decades ago, before the practice was widely employed.  Now, with the vast majority of pregnant women in modern times undergoing regular prenatal ultrasound, there is virtually no more “control group” available.  Most of the women who abstain from ultrasounds are choosing to birth outside of the system, often at home with midwives and doulas, with little to no medical interventions.  Most of these women would not want to participate in an intensely monitored clinical study.


How ultrasound affects the body – thermal and mechanical

Ultrasound frequencies can affect the body in several ways.  As stated earlier, mechanical waves moving through a medium (in this case, human tissue) cause a type of disturbance and friction.  The vibrations are absorbed to some extent by the tissues they pass through, creating a thermal effect, which can increase tissue temperature.  For sensitive tissues (like fetal tissue), this temperature rise can cause harm if the heightened temperature is sustained for a period of time.

In addition to thermal effects, there are also mechanical effects caused by the physical vibration of the tissues.  At higher intensities, this can result in a complication called cavitation, where gas bubbles within tissue begin oscillating, and either growing in size or collapsing, resulting in sudden and significant tissue heating.  This is not considered to be a potential danger in fetal ultrasound, since the baby’s body does not contain gases in the lungs or intestines, since they haven’t yet been exposed to  the gaseous environment outside the womb.  However, it is still considered to be a rare possibility, and at the higher intensities used in therapeutic procedures, ultrasound is known to cause DNA double-strand breaks.

Modern ultrasound machines are designed to guard against these potential side effects by monitoring the thermal index (TI) and mechanical index (MI), which help gauge the potential for thermal effects and cavitation, and medical practitioners should be trained to keep these at low levels.  Fetal ultrasound procedures are not considered to be high risk for these complications, due to relatively short exposure durations (usually 15-45 minutes per session), as well as non-continuous exposure where the beam is moved around often, and not focused on the same part of the baby’s body for very long.

Unfortunately, common labor and delivery procedures in hospitals in modern times bring another, much longer duration exposure source: continuous electronic fetal monitoring (EFM).  This is where a Doppler ultrasound device is attached to the laboring woman’s belly for the entire duration of her labor, to monitor her uterine contractions and the baby’s heartbeat.  Combined with longer average labor durations in modern women, this means that the baby can be exposed to ultrasound frequencies continuously for 7-18 hours or longer.  Although this practice is now common, even in low-risk pregnancies, there is almost no evidence that it increases positive outcomes in low-risk or even high-risk pregnancies.

A research paper published in 2020 hypothesizes that continuous electronic fetal monitoring during prolonged labors may increase the incidence of autism spectrum disorder (ASD) in children.  The routine use of EFM does seem to correlate with the unexplained increase in autistic symptoms in babies and children, and is worthy of consideration as one potential cause, most likely in combination with the increase of other types of interventions and toxic exposure sources.


A few more ultrasound risks to consider

Another considerable risk of both prenatal ultrasound and continuous electronic fetal monitoring is the potential for inaccuracies, and the unnecessary interventions that may follow.

Fetal ultrasound during pregnancy can sometimes result in incorrect interpretations and diagnostic inaccuracies.  This can cause a lot of stress for the parents, and even inappropriate medical interventions like premature induction or C-section. If an ultrasound detects a potential abnormality, this can cause significant anxiety for the parents, even if the finding later turns out to be benign or incorrect.  Ultrasounds are especially notorious for misjudging the size or weight of the baby, which may cause the parents to worry if the baby is said to be too small for its gestational age, or too large for a natural vaginal birth.

Electronic fetal monitoring can be affected by maternal movement or obesity, leading to inaccurate readings.  If a reading falsely detects signs of fetal distress, it may result in an unnecessary C-section or other intervention that interrupts the natural progression of labor and birth, resulting in stress and trauma for the mother and baby.

One final risk that’s important to note is exposure to actual electromagnetic fields from fetal ultrasound.  Although the frequencies that directly penetrate the body are mechanical waves, the transducer generates these waves from an electric current.  If this transducer is placed on the mother’s body, she and her baby are being exposed to these ambient electric fields, which will penetrate to some extent.  We know that babies, especially in utero, are highly sensitive to EMFs, and close exposure may impact their development.  Each prenatal ultrasound will expose the very young fetus to 15-45 minutes of electric fields, which will compound the stress from the mechanical waves themselves. Then if continuous EFM is used during labor, that’s a major EMF exposure source during the sensitive and delicate window of labor and birth, during which the mother and baby are already stressed to the max.


Undoubtedly, there are legitimate medical reasons why you may want to use ultrasound during pregnancy and labor, and it has surely saved lives when used in medically necessary instances.  That fact does not negate the need to utilize the precautionary principle with all procedures that have inadequate safety testing, and that clearly have biological effects.






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