This post was written by our board member Dana Wilms, and originally published in June of 2010. It is such a comprehensive look at the topic of ultrasounds that we are republishing this and the other two posts in her series this week.
Written by Dana
When I was pregnant with my first child, I was taken aback by my midwife’s question about whether I would like to have an ultrasound examination. Of course I did. I had been looking forward to it since I found out I was pregnant. Why wouldn’t I?
My midwife responded by outlining some possible risks. I can’t remember what she said. I really wasn’t listening. I wanted to see my baby and to be reassured that she was ok. I didn’t want to hear that it might be dangerous or consider that the exam might find something wrong with my child. Besides, every pregnant woman with whom I was acquainted wouldn’t be having at least one ultrasound if it weren’t completely harmless, right?
Studies have not shown that prenatal ultrasound exams have definitive detrimental effect on babies’ physical or cognitive development. But there is evidence to suggest there may be reason for concern. A Cochrane Review of studies on Doppler ultrasound in pregnancy summarizes its findings in this way:
Routine Doppler Ultrasound in pregnancy does not have health benefits for women or babies, and may do some harm.” [1].
I was surprised to learn that the Society of Obstetricians and Gynaecologists of Canada (SOGC)[2], Health Canada[3], and also the U.S. Federal Drug Administration (FDA)[4] and American Institute of Ultrasound in Medicine (AIUM)[5], all advise- some with strongly worded statements- against non-medical use of ultrasound in pregnancy.
These organizations’ concerns include tissue overheating and something called cavitation. I will discuss these and a number of other considerations in Part II of this series.
About Ultrasound in Pregnancy
Obstetric Sonogram- A transducer wand is moved around on the pregnant woman’s abdomen. It emits high frequency pulsed sound waves which, when they bounce back to the transducer from the tissues within, are translated into moving images. Machine intensity can be set to varying levels by the adjustment of settings such as frequency, and is influenced by how long the sound waves are focused on one area (dwell time) and whether the sound waves are pulsed or continuous. The higher the frequency of a sound wave, the sharper the image, but fainter because human tissues absorb higher frequency sound waves more readily.[6]
Transvaginal Obstetric Sonogram- The transducer wand is modified for use inside the vagina. This type of ultrasound offers better images due to the closer proximity to the uterus. Exposure levels are accordingly greater.
Fetal Doppler- A hand held unit similar to sonogram, and whose transducer emits a continuous high-frequency sound wave. The machine translates the echo of the sound waves into an audible representation of the fetal heartbeat. Fetal Doppler settings such as frequency are fixed.
Non-medical Ultrasound- These scans use the same technology as obstetric (2-D) ultrasound but the waves, which are sent at different angles, are compiled by sophisticated software into a highly defined still (3-D) and moving (4-D) images of the unborn child. They provide keepsakes for the parents.
Part II- Overheating and Cavitation: Why Health Canada, SOGC, the FDA and others are concerned…
1. Bricker L, Neilson JP. Routine Doppler ultrasound in pregnancy. Cochrane Database of Systematic Reviews 2000, Issue 2. Art. No.: CD001450. DOI: 10.1002/14651858.CD001450.pub2 (abstract accessed May 30, 2010)
2.Van den Hof, M. C. & Bly, S. (April 2007). Non-Medical Use of Fetal Ultrasound. J Obstet Gynaecol Can 2007; 29(4):364-365, No. 191. Retrieved June 13, 2010 from http://www.sogc.org/guidelines/documents/191E-PS-April2007.pdf.
3.Health Canada. (November 2003). Fetal Ultrasound for Keepsake Video. In It’s Your Health. Retrieved June 13, 2010 from http://www.hc-sc.gc.ca/hl-vs/alt_formats/pacrb-dgapcr/pdf/iyh-vsv/med/ultrasound-echographie-eng.pdf
4. U.S. Food and Drug Administration. (March 2008). Avoid Fetal “Keepsake” Images, Heartbeat Monitors. In FDA Consumer Health Information. Retrieved June 18, 2010 from http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm095508.htm
5. American Institute of Ultrasound in Medicine. (March 2007). Prudent Use in Obstetrics. Official Statements. Retrieved June 13, 2010 from http://aium.org/publications/statements.aspx
6. Physics 24/7, Physics Tutorial: Ultrasound Physics. Retrieved June 13, 2010 from http://www.physics247.com/physics-tutorial/ultrasound-physics.shtml
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