Wednesday February 3 2010
Ultrasound is the safest way of looking at the developing baby
“Parents-to-be should weigh the possible risks of going for non-essential scans purely to get keepsake pictures of their unborn babies,” BBC News reported. It said that while ultrasound scans are “entirely justifiable and safe, the Health Protection Agency (HPA) is concerned about ‘boutique’ scanning”.
This is good advice and the most appropriate that can be offered at the current time. Ultrasound has been safely used for diagnostic purposes for 50 years and is an important tool in many areas of medicine. However, with the increasing use of ultrasound for unnecessary souvenir pictures (non-routine antenatal scans) unknown risks may be introduced. As the HPA states, further research is needed to clarify these uncertainties. In the meantime, parents should weigh up these unknown risks against the benefits of having a keepsake enhanced photo of their developing baby.
Where does the news come from?
The advice regarding these souvenir keepsake images or ‘real time’ ultrasound scans that have no diagnostic benefit has been issued by the HPA.
The advice is based on a review of the evidence on the health effects of ultrasound (frequency above 20 kilohertz) and infrasound (frequency below 20 kilohertz). The review was carried out by the independent Advisory Group on Non-Ionising Radiation (AGNIR), which reports to the HPA.
The main finding is that there is no evidence that ultrasound increases the risk of mortality or cancer to the developing foetus or newborn baby. However, there are some unconfirmed reports that ultrasound could affect the developing nervous system, potentially affecting what would be the child’s natural handedness (whether they are right or left handed).
Compared to diagnostic scans that provide a basic image and opportunity for measurements of the baby’s growth and development, souvenir scans produce detailed 3D facial images or recordings of the baby’s movement in the womb and require prolonged and more intense ultrasound exposure.
What does the AGNIR report say?
The main points of the report are:
- When used for diagnostic medical purposes, which are generally infrequent and for short periods of time, ultrasound does not cause heating or cavitation damage (formation of cavities) in biological tissues, as may be seen with higher levels of exposure.
- A single study in pregnant mice has observed that ultrasound at levels used in medical practice affected the developing nerve cells in the unborn mouse brain. However, the significance of these changes is not known and the study has not been repeated.
- Ultrasound evidence in humans has mainly been concerned with in utero (within the womb) exposures. These studies have found no evidence that ultrasound affects mortality around the time of pregnancy or birth, or has any effect on childhood cancers. In randomised-controlled trials there has been ‘weak evidence’ that it may affect whether a child is right or left handed (known as handedness), which the reviewers say may be the result of confounding, rather than actual causation.
- When looking at the available evidence for the health effects of low frequency infrasound, (produced by aircraft, trains, thunderstorms, wind, waves and certain machines) there is sparse research. There are also no confirmed biological effects, although at levels above 140dB, hearing damage can occur, for example ear pain or eardrum rupture. Infrasound also has no clear physiological or behavioural effects on humans. Overall, the researchers consider there to be little evidence that infrasound exposure affects humans and no information on its long-term effects.
- Although there are recognised adverse effects from overexposure to ultrasound and infrasound, guidelines and protocols are in place to minimise or avoid this when it is used for medical purposes. Despite there being “no established evidence of specific hazards” however, there is too little evidence to draw firm conclusions about its long-term effects.
- When regarding diagnostically unnecessary souvenir foetal imaging scans, the unconfirmed reports of possible neurological effects mean there is a need for further research into possible adverse effects.
What are the conclusions of the report and HPA?
AGNIR says there is no conclusive evidence that ultrasound is dangerous to the developing baby. However, further research is needed to determine if there are any long-term adverse health effects. The chairman of AGNIR, Professor Anthony Swerdlow, said: ‘Ultrasound has been widely used in medical practice for 50 years, and there is no established evidence of specific hazards from diagnostic exposures. However, in the light of the widespread use of ultrasound in medical practice, its increasing commercial use for souvenir foetal imaging and the unconfirmed indications of possible neurological effects on the foetus, there is a need for further research on whether there are any long-term adverse effects of diagnostic ultrasound.
In response, the HPA said “parents-to-be should not hesitate to continue taking advantage of ultrasound scans for diagnostic purposes. However they should consider the uncertainties when deciding whether to have ultrasound scans that do not have a defined diagnostic benefit and provide only keepsake images or ‘real time' scans”.
Ultrasound has a long history of use in medical, surgical and antenatal care. Ultrasound images are produced from echoes formed when high frequency sound waves bounce off organs in the body.
Different tissues in the body are characterised by differences in amplitude, arrival times and frequency of echoes, with highly reflective structures such as bone giving the brightest spots on the ultrasound scan. In pregnancy, ultrasound remains the safest way of looking at the developing baby without exposing the mother or baby to the risks of radiation.
As the HPA says, there is little evidence of the longer-term health effects of ultrasound exposure to developing babies. However, the fact that antenatal ultrasounds have been used for several decades without any apparent ill effects is promising. The evidence of a neurological effect of ultrasound comes from a few animal and human studies that are viewed as inconclusive by the HPA.
Expectant parents can be reassured that routine diagnostic ultrasound scans (performed at 10-13 and 18-20 weeks of pregnancy) are safe. They can provide the baby’s definite gestational age, identify multiple pregnancies, inform about the baby’s growth, placental health and identify any developmental or structural abnormalities.
Outside of pregnancy, people should also not be concerned when undergoing ultrasounds to help with the diagnosis of medical conditions. However, souvenir scans, which provide detailed lifelike images of the developing baby as keepsakes for the parents, serve no diagnostic or clinical purpose. Compared to diagnostic scans, whether as part of antenatal or medical care, souvenir scans require prolonged and more intense ultrasound exposure. As such, they represent a potential risk to the developing baby that cannot be weighed against any necessary benefit.
The HPA advises that although there is no clear evidence that souvenir scans are harmful to the foetus, “parents-to-be must decide for themselves if they wish to have souvenir scans and balance the benefits against the possibility of unconfirmed risks to the unborn child”. This is sensible advice and the most appropriate offered at the current time.
Research into the safety of ultrasound is continuing, both in the UK and internationally.