What types of imaging are permissible in pregnancy?
A variety of imaging modalities, including those that use ionizing radiation and those that do not, can be used in pregnant patients. Pregnant patients are consented for possible risks to themselves and their unborn children before the imaging is performed. MRI and US are generally considered as safe in pregnancy. Radiography, CT, and fluoroscopy, although delivering ionizing radiation, can be used judiciously when the potential diagnostic benefits outweigh the potential risks of radiation exposure. The gravid abdomen can be shielded with lead drapes for imaging of the chest, and in early pregnancy the pelvis can be shielded if abdominal imaging is required. Nuclear medicine examinations are used only if absolutely necessary and are customized to administer decreased doses of radiotracer. The use of intravenous contrast is limited in pregnancy, as both gadolinium-based MRI contrast agents and iodinated CT contrast agents cross the placenta  . Gadolinium-based MRI contrast agents are typically not administered to pregnant patients as they are excreted by the fetal kidneys into the amniotic fluid and can remain there for an unspecified period of time. Animal studies have shown teratogenic effects from gadolinium exposure, but evidence in humans is limited and has shown no adverse effects. If necessary, iodinated CT contrast is used as it can be excreted by the maternal kidneys. However, free iodine that enters the fetal circulation can affect fetal thyroid function. Neonates of mothers who have received iodinated contrast media during pregnancy undergo thyroid function testing during the first week of life to identify any potential issues.