Ultrasounds in Prenatal Care – Are they safe?

Ultrasounds are the norm in prenatal care, but is it really harmless for baby?My first son was born with a birth defect which nearly killed him.  His doctors told me there was no clear cause, that sometimes these things just happen.  You can read more about my experience here.

When I became pregnant with my second child, I began to realize how terrified I was at the thought of going through an entire pregnancy and child birth again.  According to my doctors, I was at the mercy of nature, a proverbial game of Russian Roulette where I must hope the odds are in my and my unborn child’s favor.  I simply don’t believe that.  My experience has shown me that everything a pregnant mother eats, breathes, thinks and feels impacts how our children develop and who they become.

All throughout my prenatal care with #2, I made sure to research everything and ask a lot of questions.  I think I annoyed my doctors with every visit!  After discussing my first pregnancy with my doctors, they recommended I get a Level 2 ultrasound as a precaution.  They told me it would be a forty minute ultrasound with a special technician, which did not feel right to me as I was not considered a high risk pregnancy and the odds of my second child having the same problem were next to zero.  I asked them for some time to look into it before scheduling the appointment.

What exactly is an ultrasound?

Ultrasound waves are sound waves so high in frequency they are inaudible to the human ear.   These waves pass from the hand-held piece called a transducer (or if you’re really lucky, a probe) into the human body and bounce off different types of tissue back to the transducer, which then assembles waves into an image via a computer screen.  Higher frequency ultrasounds produce a clearer picture but cannot view that deep into the body, while lower frequencies are the opposite. Different types of scans use different types of ultrasound technology.  According to Australian Physician Dr. Sarah Buckley:

Ordinary scans use pulses of ultrasound that last only a fraction of a second, with the interval between waves being used by the machine to interpret the echo that returns. In contrast, Doppler techniques, which are used in specialized scans, fetal monitors and hand-held fetal stethoscopes (“sonicaids”) feature continuous waves, giving much higher levels of exposure than ‘pulsed’ ultrasound. Many women do not realize that the small machines used to listen to their baby’s heartbeat are actually using Doppler ultrasound, although with fairly low exposure levels.

The History of Ultrasounds in Prenatal Care.

The Food and Drug Administration approved ultrasound as safe to use by passing a law in 1976 which was based on studies conducted on technology available at that time.  Advances in technology have brought new and better machines to the market, utilizing greater intensity (also known as acoustic output) overall.  Due to the new technology, in 1991 the US government increased the allowable intensity of the ultrasound wave nearly eight times the previous allowable limit.  (Source)  According to the National Council on Radiation Protection and Measurement, epidemiological studies have not been conducted regarding ultrasound safety since before 1992 because, “It can take many years to plan, execute and analyze a scientific study of the effects of ultrasound on the human population… As a result, virtually all of the studies so far of in utero ultrasound exposure tracked babies exposed to the earlier, lower acoustic output levels, not the higher levels allowed since 1991.”  (Source)

In current obstetrical care, diagnostic ultrasounds are performed:

  • to confirm a normal pregnancy
  • to determine the approximate due date by measuring the size of the fetus
  • to check for problems with the placenta, uterus, ovaries, etc.
  • to check baby’s heart rate
  • to determine the sex of the baby

When I was pregnant with my first son in 2008, I received one ultrasound scan at 20 weeks to determine the sex.  (This scan did not show the problems with his bladder or kidneys, nor did it tell us the correct sex!) With my second pregnancy at a new medical practice in 2012, I had four ultrasounds, most of them only a minute or two for random, non-emergency reasons.  I had declined two more over the course of being pregnant, which would have brought my total to six.  Note that none of these scans provided crucial information that we wouldn’t have been able to determine without the scans.  Studies have shown that calculating the due date based on menstrual cycle is just as effective as using an ultrasound scan.  (Source.)

With the increase in use of ultrasound scans by physicians, it seems implied that they are entirely safe.

What do studies show about the safety of ultrasound?

According to the American Pregnancy Association:

“There is not a recommended number of ultrasounds that should be performed during routine prenatal care. Because ultrasound should only be used when medically indicated, many healthy pregnancies will not require ultrasound. The average number of ultrasounds varies with each healthcare provider.”

As you can see, it is recommended to keep the number of ultrasounds performed at a minimum.  What is the reason for concern?

There are three known adverse effects which can occur during an ultrasound.

  • Heat.  The sonar wave can cause the tissues being scanned to rise in temperature, heating bone to a higher degree than soft tissue or fluid.  For this reason, the brain is more at risk because it is encased by the skull, which is developed in the second trimester.  The chance of the bone heating up the brain from ultrasound increases throughout the pregnancy as the fetal bone density increases.  Studies have shown temperature increases reach high levels after only 30 seconds of a pulsed Dopplar scan.  The intensity of modern machines are very capable of causing a dangerous temperature rise, it is the technician who is trained to assess the risk vs. benefit when conducting a scan and prevent possible damage to a fetus.  Source.
  • Cavitation.  Cavitation occurs when sound waves pass through an area with an air pocket. Because infants do not breathe air, this is not so much of a concern, however the fetus does receive oxygen from the mother’s blood.  Not enough science exists to say there is no cavitation occurring in a fetus as a result of an ultrasound.  Cavitation can cause release of free radicals and other toxic chemicals which can result in genetic defects.
  • Acoustic Streaming.  When ultrasound waves pass through liquid, it can cause a wave-like effect called acoustic streaming.  This can happen in amniotic fluid as well as the fetus’s blood.  When the liquid waves approach solid objects, platelets can be damaged and blood-clotting problems can occur.  (Source)

While science has not provided a clear link between ultrasound and birth defects, it is important to remember that no studies have been conducted since before 1992 which is before the intensity of modern machines increased.  Studies such as this, however, have shown fetal damage to mice pups after thirty minutes of ultrasound at embryonic day 14.5.  Findings were that the exposed mice were less interested in social interaction and were more likely to display hyperactive behavior in the presence of an unfamiliar mouse.  There are many studies which suggests possible adverse effects from ultrasound exposure.

Dr. Kelly Brogan also brings and interesting point in this article, stating that over the last two decades increases  in the number of vaccinations given in a normal schedule as well as introduction of GMO foods leaves fetuses more at risk for potential developmental problems when combined with increase in routine ultrasounds.

When are ultrasounds necessary?

Initially, ultrasounds were only used in prenatal care to look into potential problems.  For a high-risk pregnancy, ultrasounds are a great tool for doctors to check on the fetus and make sure everything is okay.  From all of the studies I have read, it really comes down to weighing the risk vs. the benefit.  There are risks associated with ultrasounds and the long term effects are unknown.  A scientific analysis published in the European Journal of Ultrasound concluded:

“While ultrasound is a sound wave which can produce mechanical effects and temperature elevation in tissues that it traverses, the risk to human fetuses when using diagnostic ultrasound appears to be minimal if certain rules are followed, such as performing a scan when medically indicated, and observing the ALARA principle (using the lowest output power consistent with acquiring the necessary diagnostic information and keeping the exposure time as low as possible for accurate diagnosis).”

Per the U.S. FDA:

“Even though there are no known risks of ultrasound imaging, it can produce effects on the body. When ultrasound enters the body, it heats the tissues slightly. In some cases, it can also produce small pockets of gas in body fluids or tissues (cavitation). The long-term effects of tissue heating and cavitation are not known. Because of the particular concern for fetal exposures, national and international organizations have advocated prudent use of ultrasound imaging. Furthermore, the use of diagnostic ultrasound for non-medical purposes such as fetal keepsake videos has been discouraged.”

It seems that most scientists and government regulatory agencies agree; the less a fetus is exposed to ultrasound waves, the better.  The medical practice I went to with my second pregnancy seemed to have little discretion with using ultrasound technology.  It is easy to say that ultrasounds do not cause damage based on all the healthy babies that are born, however with the increases in autism and childhood diseases, all with unknown causes, we should tread lightly and be as precautionary as we can.

The amount of toxins and stressors a fetus is exposed to this day in age is unprecedented, and it doesn’t stop when they are born into this world.   It is up to us as parents to be the most careful we can be in protecting them from potential harm and unnecessary danger.  In the case of ultrasounds, the fewer the better.


Brogan, Kelly MD.  “Ultrasound Risks Perils of Peeking into the Womb.”  15 December 2013.  17 July 2014.

McClintic AM1, King BH, Webb SJ, Mourad PD.  “Mice exposed to diagnostic ultrasound in utero are less social and more active in social situations relative to controls.”  8 November 2013.  17 July 2014.

Abramowicz JS, Kremkau FW, Merz E.  “Obstetrical Ultrasound: Can the Fetus Hear the Wave and Feel the Heat?” 14 June 2012.  17 July 2014. http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/ucm115357.htm

Miller, Douglas L. Ph.D.  “Safety Assurance in Obstetrical Ultrasound”  Semin Ultrasound CT MR. Apr 2008.  17 July 2014.


Houston, L. E., Odibo, A. O. and Macones, G. A. (2009), The safety of obstetrical ultrasound: a review. Prenat. Diagn., 29: 1204–1212. doi: 10.1002/pd.2392 http://onlinelibrary.wiley.com/doi/10.1002/pd.2392/abstract;jsessionid=2808660E43CE5072BEFB1311760D2339.f02t03

Barnett SB.  “Intracranial temperature elevation from diagnostic ultrasound.” 2001.  http://www.ncbi.nlm.nih.gov/pubmed/11476919/

Charach R1, Abramowicz J, Shoham-Vardi I, Sheiner E. “Is it safe for my baby? Acoustic exposure of diagnostic ultrasound.”  July 2011.  18 July 2014.  http://www.ncbi.nlm.nih.gov/pubmed/21874769

Barnett SB1, Rott HD, ter Haar GR, Ziskin MC, Maeda K.  “The sensitivity of biological tissue to ultrasound.”  1997.  18 July 2014.


Abramowicz JS1, Barnett SB, Duck FA, Edmonds PD, Hynynen KH, Ziskin MC.  “Fetal Thermal Effects of Diagnostic Ultrasound.”   27 April 2008.  18 July 2014.


Marinac-Dabic D1, Krulewitch CJ, Moore RM Jr. “The safety of prenatal ultrasound exposure in human studies.”  May 2002.  18 July 2014.

http://www.ncbi.nlm.nih.gov/pubmed/12071478 http://www.ncrponline.org/Publications/Reports/Misc_PDFs/Ultrasound%20Summary–NCRP.pdf




6 thoughts on “Ultrasounds in Prenatal Care – Are they safe?

  1. How insightful! It is insane what we allow our bodies to go through with absolutely no questioning. We need change. Big time. …it all starts with knowledge. Thank you for sharing.


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