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Is having an ultrasound examination safe for my baby?

Pregnancy Dr Minke Burke Director
Women can nowadays expect to have between 2 and 3 ultrasound scans during their pregnancy. It is a great way to visualise your baby, and is considered safe. What do we know about the potential harmful effects it may have on your growing baby?

Ultrasound has been used for over 50 years in obstetrics.  Initially it helped answering basic questions like:

  1. Is there a pregnancy and is the baby alive?
  2. Is there only one baby?
  3. Where is the placenta?

Over the years the technology of this modality has advanced dramatically and ultrasound is now capable of displaying fetal anatomic structures in great detail.  Hand in hand with this enhanced ultrasound technology, our knowledge in fetal anatomy has significantly improved, allowing for early diagnosis of many fetal anomalies.  It is wise to keep in mind though, that ultrasound is not able to pick up all abnormalities.

Ultrasound uses sound waves that are transmitted by the ultrasound probe or transducer.  A gel is applied between your skin and the ultrasound probe and serves as a conductor to facilitate transmission of the ultrasound beam.  The ultrasound waves travel from the transducer through the tissues and back again to the transducer.  Computer software is used to process and manipulate the sound signals, eventually displaying an image on the screen.  The ultrasound wave journey from the probe and back is dependent on the characteristics of each tissue in relation to its surroundings, as some of this ultrasound wave is being absorbed, reflected back or passed through.

So how can these sound waves be potentially harmful?  The potential hazards are in the tissue specific absorption of the sound waves, the nature and characteristics of individual tissues (like kidney tissue versus bone) and the speed (frequency) of sound beams, to name a few.  The potential harmful ultrasound effects on the baby are called bio effects and are divided into are “thermal” or “non thermal” effects.  Absorption of sound waves or concentrated sound waves can cause tissue to heat up.  This is measured by the “Thermal Index”.  You can imagine that the baby in the first trimester is more susceptible to potential warming.  We know that the normal “grey-scale” ultrasound is extremely unlikely to increase the fetal temperature during a routine ultrasound examination.  However, Doppler ultrasound has a considerable heat formation capability and is generally not used in the first trimester, and with caution in second and third trimester.  Other potential tissue damage is not by heating but by pressure of the sound waves  (mechanical interaction) or formation of gas bubbles within tissues.  Both these mechanisms cause cell damage.  The “Mechanical Index” estimates this cell damage.  Mechanical effects are unlikely to occur in obstetric ultrasound because of the absence of gas bodies or contrast medium.

There have been many studies trying to identify a link between ultrasound and,  for example, low birth weight, chromosomal and structural abnormalities, leukemia and even left handedness.  To date no such link has been demonstrated.  Even though this sounds very reassuring, we follow the ALARA (as low as reasonably possible) principle and the recommendation of The Australian Society for Ultrasound in Medicine.  This means that we should only perform an ultrasound when indicated, and minimise the exposure time and intensity.

At Alana you can be reassured that in our expert hands we have your baby’s safety in mind during your ultrasound examination.