Understanding Ultrasound

July 23, 2013

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What is ultrasound?

Ultrasound is a technology that works similarly to the way bats use echoing sound waves to fly and hunt at night. Ultrasounds within the context of pregnancy and birth are used to get information by creating images of the baby, the baby or placenta’s blood flow, or listening to the baby’s pulse. The ultrasound wand that is placed on your belly sends a beam of fast (ultra) sound waves at the baby which then bounces off of the baby’s body and back to the beam. The sonogram machine turns that information into an image of the baby. The Doppler technology turns it into an audible rhythm (and sometimes an image) of the baby’s pulse. Dopplers use constant beams of ultrasound whereas sonograms use pulsed beams of ultrasound. Depending on the reason for an ultrasound at an imaging office or OBGYN office, both ultrasound and Doppler technology may be used with the same equipment (they can switch back and forth). Dopplers used in midwifery care are only used to listen to the baby’s pulse, so they are a much more primitive technology and lower intensity than the Dopplers in hospitals.

Is ultrasound technology safe?

The simple answer is that the safety of using any ultrasound technology on pregnant mamas and babies has never been clearly established. In other words, no one can say for certain that it is safe to use ultrasound equipment on pregnant women and their babies. Additionally, evidence shows that routine use of ultrasound in low-risk pregnancies DOES NOT improve outcomes for either mother or baby.

What are the risks?

The ultrasound beam can and does cause a temperature increase in the tissue where the ultrasound beam is aimed (this is why ultrasound is sometimes used on joints and other areas in physical therapy or by athletes with injuries), and in pregnancy the beam happens to be aimed at your baby. No studies have been done to ascertain how much of a temperature shift occurs when used on babies in the womb. There is also the concern that the high frequency sound waves may interfere with the loosely developed embryo through a cavitation process where small pockets of gas in tissues vibrate and then collapse. Again, the significance of this is not well understood. Some studies have been done on both animals and humans, with some findings that are noteworthy. Studies on mice have shown that exposure to ultrasound can interfere with the development of the nervous system, the migration of brain cells to their correct locations, can slow down the rate of cell division in the intestines. In her article “Ultrasound Scans- Cause For Concern”, Sarah Buckley lists these as the possible adverse effects of ultrasound:

• premature ovulation
• preterm labour or miscarriage
• low birth weight
• poorer condition at birth
• perinatal death
• dyslexia
• delayed speech development
• less right-handedness (seen as a marker of damage to the developing brain)

There are also the social and psychological risks of ultrasound. If an abnormality is suspected during an ultrasound and follow up is recommended, women then have to deal with the time (sometimes weeks) before getting more conclusive information about her baby and her options. This time can be incredibly stressful and confusing for women and their families. If they are asked to do scan after scan, they may begin to feel disconnected from their baby, as if the baby belongs more to the medical industry than to her and her family. Even if nothing is found to be abnormal, the reliance on ultrasound and ultrasound technicians is yet another chance to imprint into the woman that in our culture, her knowledge of her own body and her own baby is secondary to “experts” and technology.

What are the benefits?

There is no doubt that ultrasound can be helpful in some circumstances. The problem is that most ultrasounds are not done for medically indicated reasons (learning the sex is not a medically indicated reason). Again, routine serial ultrasound scanning, meaning for every pregnancy and at regular intervals throughout the pregnancy, has not been shown to improve the outcomes for mothers or babies. Ultrasounds can be useful for many reasons though, some of which include:

– Diagnosing multiple gestations
– Getting a more accurate date if the other methods of dating are questionable
– Looking to make sure the baby is implanted in the uterus; ruling out an ectopic pregnancy
– Confirming a heart beat if it is uncertain
– Checking placental location after suspected placenta previa
– Confirming fetal position near term if it is in question
– Observing baby’s well being during postdates

Ultrasounds can also be beneficial in helping meet mental and emotional needs of some mothers. In nearly all of these circumstances, the ultrasound can be done in under 5 minutes because the technician can be told specifically WHAT THEY ARE LOOKING FOR, and then they can be done. Routine ultrasounds are not just looking for specific information about a potential issue, they are looking at all aspects of the pregnancy that are measurable, when there is nothing indicating a problem. You should know the reason you are getting an ultrasound, and it can be communicated clearly with the ultrasound technician that you want them to obtain only the information you are there for.

How is the use of ultrasound technology regulated?

The FDA regulates the maximum acoustic outputs of ultrasound machines, but allows ultrasound technicians to self regulate the power that is emitted, the type of application and the control changes. This allows technicians to greatly increase the output to levels that are known to have detrimental consequences. Also, starting in 1992, the FDA gave in to industry requests and the acoustic output was allowed to increase eight fold from 94 to 720 mW per square centimeter. It should be noted that almost all studies that have been done on the safety of fetal ultrasound use data that was collected from before the 1992 shift.

Can ultrasound technicians help lower the amount of exposure?

There have been some attempts to teach ultrasound technicians how to decrease the potential risks of ultrasound, but “approximately 70% of clinicians (physicians, sonographers, and nurses who perform ultrasound) show very poor or no knowledge of bioeffects and safety issues” (Abramowicz 2010). It is also unknown if there are cumulative effects of ultrasound either due to prolonged exposure or repeated exposure. Some women under medical care now routinely have 10 ultrasounds requested during their pregnancies which leads me to believe that mainstream care providers are not taking the unknown safety of ultrasound seriously.

If you are going to get a sonogram, make sure you have your scan done by someone experienced and open to your requests – and if you don’t have much of a choice, be prepared to be polite but firm about your questions, requests and needs. In my experience, most ultrasound techs are kind and open to concerns, and at this point have come across other families with the same concerns. Make sure they know exactly what information you do want and don’t want, ask to have the lowest intensity settings, and the shortest, most efficient scan possible.


Abramowicz, Jacques S. “Fetal Doppler: How to Keep It Safe?” Clinical Obstetrics and Gynecology 53.4 (2010): 842-50.

Alfirevic Z, Stampalija T, Gyte GML. Fetal and umbilical Doppler ultrasound in normal pregnancy. Cochrane Database of Systematic Reviews 2010, Issue 8. Art. No.: CD001450. DOI: 10.1002/14651858.CD001450.pub3.

Barnett, S. B., and D. Maulik. “Guidelines and Recommendations for Safe Use of Doppler Ultrasound in Perinatal Applications.” Journal of Maternal-Fetal and Neonatal Medicine 10.2 (2001): 75-84.

Buckley, Sarah. “Ultrasound Scans- Cause for Concern | Sarah Buckley.” Dr Sarah Buckley MD, Gentle Birth, Gentle Mothering: The Best Possible Start. Web. 23 Nov. 2011. .

Deane, Colin. “Safety of Diagnostic Ultrasound in Fetal Scanning.” CENTRUS – Ultrassonografia E Medicina Fetal. Web. 02 Nov. 2011. .

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We are mamas and midwives who decided to do birth differently– and bring others along with us. We are radical, fun to work with, and great at (lovingly) calling people on their bullshit to help move us all towards a new more beautiful world. With 12 children and over two decades of midwifery between us, we’ve learned a thing or two along the way, and Indie Birth is our space to share it all with you.

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