Dangers of Prenatal Ultrasound

The prenatal ultrasound scan is ubiquitous in today’s society. Almost every woman who chooses to give birth in the hospital gets one. Those having a homebirth may choose to forgo the scan.

We have been assured that ultrasound is safe for unborn babies, but this has not been proven. There are many factors that affect the safety of the procedure, but those factors are rarely discussed with patients.


Factors which affect safety of the procedure are temperature increase, cavitation, and sonoporation, or transient membrane permeability. Temperature increase occurs primarily at the molecular level as energy is transferred to the tissues. The amount of heating depends on the kind of tissue being exposed to the beam, the amount of time the beam is concentrated in one place, the transducer focal point and the power of the beam. Fluids such as blood, urine and amniotic fluid have an absorption rate of zero; soft tissues have a moderate absorption rate; and bone has the highest absorption rate. The amount of heating depends on the thickness of the mother’s abdominal wall, the amount of amniotic fluid, and the density of the fetal skeleton. Heating has a cumulative effect. Cavitation is caused by the vibrations produced by sound waves, and mainly involve existing micro bubbles that implode and cause a shock wave. Heated liquid shoots out of the bubbles which can also cause damage. This damage on the cellular level happens if the ultrasound is above a certain frequency, but an attempt to minimize this is made with recommendations to keep the frequency within certain parameters. A frequency of 3 MHz causes sonoporation, a process which opens channels in the cell membrane that allows nano-particles to enter. Free radicals are also created. With so many variables, it seems difficult to believe that even an experienced sonographer would be able to avoid these pitfalls. How can the operator possibly know where micro bubbles are located? They can’t be seen on the screen.


Manufacturers do have standards of operation for ultrasound machines, but there are no regulations in place for enforcement of these standards. Risks? Some studies have shown increased frequency of sister chromatin changes, genetic code switching and crossing over. Free radical damage has been observed in plasma and amniotic fluid. Heat is a known inducer of fetal malformation. A higher rate of childhood cancers and leukemia are suspected, and lower birth weight babies in some studies. Some studies suggest developmental delays are a risk as well.


For a really thorough discussion of prenatal ultrasound, see Understanding Diagnostic Tests in the Childbearing Year, Anne Frye, 7th Edition. On pages 934, 935, and 936, there are 83 reference studies on the safety, risks, and professional standards of ultrasound technology. Don’t you owe it to yourself to have all the information?

The only good reason to have an ultrasound is to check for a suspected abnormality. “Routine” screenings, checking the sex of the baby, checking fetal presentation or lie, and other non-diagnostic purposes are discouraged. As always, the choice is yours.

Pregnant Women Get More Ultrasounds Without Clear Medical Need, Wall Street Journal, July 2015. “Ultrasonogram should be used only when clinically indicated, for the shortest amount of time,” the statement said, referring to ultrasound scans, “and with the lowest level of acoustic energy compatible with an accurate diagnosis.” Now, why all these conditions? Because there is definitely concern about safety. “Doctors warn pregnant women to avoid alcohol, hot tubs, excessive stress and other potential risks to the fetus. There haven’t been similar warnings about ultrasound.”

Study Explores Prenatal Ultrasound Depth and Childhood Developmental Diagnosis, Boston University School of Medicine, February 2018. “For ultrasounds done during the first and second trimesters, among several parameters considered, one – deeper ultrasound wave penetration – was statistically associated with ASD compared to children with typical development.“ ASD is Autism Spectrum Disorders.

Many of these articles point out that doctors don’t keep up with reading medical journals, so they aren’t aware of the latest studies available. That’s why you have to educate yourselves and take this information to your doctor or midwife, if you are using those practitioners.

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