Fetal MRI Safety

Safety of Fetal MRI

United States Food and Drug Administration guidelines  require labeling of MRI devices to indicate that the safety of MRI with respect to the fetus “has not been established.” Safety concerns arise for both mother and fetus. Maternal safety concerns are the same as for a nonpregnant patient and are addressed by standard MRI screening. Fetal safety concerns are related to teratogenesis and acoustic damage.

Most studies suggest MRI during pregnancy is safe , but several animal studies have raised the possibility of teratogenetic effects in early pregnancy . Although these studies may not be applicable to humans or may represent statistical quirks, they suggest that a cautious approach to adopting the use of MRI in women during the first trimester may be advisable. The guidelines of the National Radiological Protection Board in the United Kingdom state, “It might be prudent to exclude pregnant women during the first three months of pregnancy.” An additional concern in the first trimester is the underlying relatively high rate of spontaneous abortion during this period. An MRI study could be coincidentally followed by a spontaneous abortion that might appear iatrogenic to the patient. That said, when a strong clinical indication has been established, MRI is probably still preferable to any study involving ionizing radiation 

The loud noises generated by the coils of the MR scanner as they are subjected to rapidly oscillating electromagnetic currents could potentially cause acoustic damage to the fetus. Two reports from the United Kingdom provide reassuring clinical and experimental evidence that the risk of acoustic injury is negligible. In summary, pregnant women in the second and third trimester can be reassured that MRI poses no known risk to the fetus. Although safety has not been positively established, any hazard appears negligible and is outweighed by the potential diagnostic benefit. A more cautious approach should be taken when MRI is required during the first trimester.

While the long-term safety of MRI has not been fully established, it is believed, in general, that the benefit it provides in fetal management far outweighs any theoretical risks. No adverse biological effects have been reported at the energies currently delivered with MRI.Whether or not to obtain written consent reflects institutional bias: at Children's Hospital Boston, consent is no longer obtained for performance of routine fetal MRI, while at Massachusetts General Hospital, it is. Most imaging occurs at or after 18 weeks' gestation, when fetal size and motion first allow reasonable visualization with current MRI techniques, avoiding exposure during the peak of organogenesis. Gadolinium is not administered.

Many studies have shown that fetal MRI examination is not associated with any major deleterious effects.  No health risks have been reported at field strength of 1.5-Tesla (1.5-T). No adverse outcomes have been observed in pregnant MRI workers. The Safety Committee of the Society for MRI has concluded that prenatal MRI is indicated when other nonionizing diagnostic imaging methods are inadequate or when MRI examination can provide important information that would otherwise require the use of ionizing radiation. There is currently no data regarding the level of acoustic noise experienced by the fetus during the MRI procedure. The use of gadolinium is not recommended because of the need to avoid potential deleterious effects on the fetus.  The National Radiation Protection Board and the Food and Drug Administration have approved MRI only after the first trimester. The safety of the newer techniques of diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI) , MRI spectroscopy (MRS), and functional MRI (F-MRI) has not yet been proven.