Abstract
Since the introduction of prenatal magnetic resonance imaging in 1980s, safety issues
have been discussed in numerous publications. The examination is contraindicated in
certain circumstances, as in the general population. Available fast magnetic resonance
imaging (MRI) techniques make sedation of the mother (and fetus) unnecessary. Proper
positioning of the patient is important to avoid compression of the inferior vena
cava by the pregnant uterus. Static magnetic field, radiofrequency pulses and magnetic
field gradients constitute the three hazards to the fetus examined in the MRI scanner.
High static magnetic fields are only responsible for sensory effects: vertigo, metallic
taste and magnetophosphenes. Electromagnetic radiofrequency pulses result in energy
deposition and are responsible for tissue heating during MRI. Increased temperature
is especially harmful to the fetal central nervous system. Temperature rise of 2 °C
lasting for 24 h may cause neural tube and cranio-facial abnormalities. The amount
of energy deposited in a patient over time is reflected by specific absorption rate
(SAR). In a study using SAR of 4.0 W/kg (the upper limit in general clinical MRI imaging)
no maternal temperature changes were detected. MRI is unlikely to result in significant
temperature changes provided that temperature and humidity in the MRI suite are kept
within the recommended limits: of less than 24 degrees °C and below 60%, respectively.
MRI generates noise. Water – the main component of the amniotic fluid – reduces sound
intensity of approximately 30 dB. It is unlikely that the MRI scan would harm the
fetus hearing and such harmful effects have not been observed in follow-up studies.
The mother is protected by headphones with music, which also has a calming effect
in case of claustrophobia and general anxiety. Harmful influence of MRI on organogenesis
in the first trimester of pregnancy has not been described at the clinically used
magnetic field strengths. In most centers, gadolinium is not used for fetal imaging.
If it is used, it is for maternal reasons, if the benefits outweigh the potential
risk. Last but not least, it is important to perform fetal MRI in specialized centers.
Staff experience both in performing and interpreting the study is crucial to make
the examination as short and conclusive as possible.
Keywords
MRI - fetus - safety
