Safety of Ultrasound in Pregnancy Reference: RCOG

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Safety of Ultrasound in PregnancyReference
RCOG TOG Journal
Deepa Jacob
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Key content

• General perception is that ultrasound has no
  adverse effects.
• Laboratory studies has shown potential clinical
  significance.
• Bioeffects can be either thermal or mechanical.
• Safety indices are thermal index and mechanical
  index

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ALARAAs Low As Reasonably Achievable

• ALARA principle
• Lowest acoustic power output
• Shortest duration
• Least exposure to sensitive target tissues
• These can reduce biohazards.

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Safety Guidelines

• British Medical Ultrasound Society-BMUS
• European Federation of Societies for Ultrasound
  in Medicine and Biology-EFSUMB
• World Federation for Ultrasound in Medicine and
  Biology-WFUMB

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• Ultrasound is a type of mechanical energy that
  penetrates tissue as an oscillating wave of
  alternating pressure
• Measured in megapascals
• B-Mode, M-Mode and 3D energy is transmitted in
  pulses
• Doppler- fixed beam for fixed target tissue

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Factors affecting hazard potential of Ultrasound

• Ultrasound exposure
• Energy/power emitted by the
  equipment
• Target Tissue Composition
• Proteinaceous tissue----THERMAL
  injury
• Fluid Gas content------MECHANICAL
  injury
• Tissue susceptibility
• Rapidly proliferating fetal and
  embryonic tissue more
• Adult tissues less susceptible
• Clinical settings
• Type of transducer,
• depth of penetration,
• overlying layers of tissues

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Thermal Effects

• An increase in tissue temperature is the most
  worrying bioeffect.
• Alteration of Equipment settings and prolonged
  exposure can result in thermal effects
• Liquids and soft tissue energy dissipates
  longitudinally in all directions
• Bone spread to surrounding tissue. ( Important to
  developing brain and spinal cord )

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Thermal effects

• Temperature elevation occurs when USS energy is
  converted to thermal energy.
• Lab studies shown that a temp elevation of 4 ºC
  lasting for five minutes or more is potentially
  hazardous.
• Temperature elevations of 1.5ºC present no
  hazard.
• Caution is warranted in a febrile mother.
• Beware of faulty equipment also.

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Thermal effects

• Fixed target and fixed transducer result in
  higher temperature rise.
• (This is relevant in first trimester scanning)
• Fetal CNS is the most susceptible
• Hyperthermia can result in neural tube defects
• Doppler USS devices can cause significant temp
  rise.

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Mechanical effects
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Mechanical effects

• Cavitation injury
• Development of gas bubbles
• Tissues containing gas pockets are vulnerable
• Contrast agents increase risk

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Thermal index

• Indicator of temp elevation
• Acoustic power required to rise 1ºc temp
• TIS ( soft tissue)
• TIB ( Bone)
• TIS LESS THAN 8 WEEKS
• TI 0.5 recommended

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MECHANICAL INDEX

• Indicator of cavitation injury
• MI 0.3 recommended
• More than 0.3 minor damage to neonatal
  lung/intestine possible

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studies

• Newnham et al
• RCT multiple exposure IUGR
• Follow up up to 8 years.
• No difference in development
• Swedish study
• Increase in non right-handedness
• Boys
• Salvesan and Eik-Nes
• No decreased BW, No increase malformation
• No evidence of increase congenital
  malformation

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Conclusion

• General consensus is that USS is safe in
  pregnancy
• No sustained long term effects
• The minimum possible acoustic power output,
  duration and exposure to sensitive tissues which
  gave the optimum diagnostic information should
  always be used to reduce biohazards

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• Do you know the greatest danger to the fetus in
  prenatal diagnostic ultrasound?

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Misdiagnosis
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Thankyou