Medical imaging in pregnancy

Medical imaging in pregnancy may be indicated because of pregnancy complications, intercurrent diseases or routine prenatal care. Options for medical imaging in pregnancy include the following: Magnetic resonance imaging (MRI) without MRI contrast agents as well as obstetric ultrasonography are not associated with any risk for the mother or the fetus and are the imaging techniques of choice for pregnant women. Projectional radiography, X-ray computed tomography and nuclear medicine result in some degree of ionizing radiation exposure but have with a few exceptions much lower radiation doses than what is associated with fetal harm. They are indicated when ultrasonography or MRI is not readily available or not feasible for the diagnostic question at hand. Radiocontrast agents, when orally administered, are harmless. Intravenous administration of iodinated radiocontrast agents can cross the placenta and enter the fetal circulation, but animal studies have reported no teratogenic or mutagenic effects from its use. There have been theoretical concerns about the potential harm of free iodide on the fetal thyroid gland, but multiple studies have shown that a single dose of intravenously administered iodinated contrast medium to a pregnant mother has no effect on neonatal thyroid function. Nevertheless, it generally is recommended that radiocontrast only be used if required to obtain additional diagnostic information that will improve the care of the fetus or mother. Magnetic resonance imaging (MRI), without MRI contrast agents, is not associated with any risk for the mother or the fetus, and together with medical ultrasonography, it is the technique of choice for medical imaging in pregnancy. For the first trimester, no known literature has documented specific adverse effects in human embryos or fetuses exposed to non-contrast MRI during the first trimester. During the second and third trimesters, there is some evidence to support the absence of risk, including a retrospective study of 1737 prenatally exposed children, showing no significant difference in hearing, motor skills, or functional measures after a mean follow-up time of 2 years.