MRI Contrast Agents and Pregnant Patients
Administration of Contrast Media to Pregnant or Potentially Pregnant Patients
Studies of low-molecular weight water-soluble extracellular substances such as iodinated diagnostic and gadolinium-based magnetic resonance (MR) contrast media in pregnancy have been limited, and their effects on the human embryo or fetus are incompletely understood. Iodinated diagnostic contrast media have been shown to cross the human placenta and enter the fetus in measurable quantities . A standard gadolinium-based MR contrast medium has been shown to cross the placenta in primates and appear within the fetal bladder within 11 minutes after intravenous administration . It must be assumed that all iodinated and gadolinium-based contrast media behave in a similar fashion and cross the blood-placental barrier into the fetus.
After entering the fetal blood stream, these agents will be excreted via the urine into the amniotic fluid and be subsequently swallowed by the fetus . It is then possible that a small amount will be absorbed from the gut of the fetus and the rest eliminated back into the amniotic fluid, the entire cycle being repeated innumerable times.
In the study in primates, placental enhancement could be detected up to 2 hours following the intravenous (IV) administration of gadopentetate dimeglumine. When gadopentetate dimeglumine was injected directly into the amniotic cavity, it was still conspicuous at 1 hour after administration . There are no data available to assess the rate of clearance of contrast media from the amniotic fluid.
Iodinated X-Ray Contrast Media (Ionic and Nonionic)
Diagnostic iodinated contrast media have been shown to cross the human placenta and enter the fetus when given in usual clinical doses. In-vivo tests in animals have shown no evidence of either mutagenic or teratogenic effects with low-osmolality contrast media (LOCM). No adequate and well-controlled teratogenic studies of the effects of these media in pregnant women have been performed.
In conjunction with the existing ACR policy for the use of ionizing radiation in pregnant women, we recommend that all imaging facilities should have polices and procedures to attempt to identify pregnant patients prior to the performance of any examination involving ionizing radiation to determine the medical necessity for the administration of iodinated contrast media. If a patient is known to be pregnant, both the potential radiation risk and the potential added risks of contrast media should be considered before proceeding with the study.
While it is not possible to conclude that iodinated contrast media present a definite risk to the fetus, there is insufficient evidence to conclude that they pose no risk. Consequently, the Committee on Drugs and Contrast Media recommends the following:
A. The radiologist should confer with the referring physician and document in the radiology report or the patient’s medical record the following:
1. That the information requested cannot be acquired without contrast administration or via another image modality (e.g., ultrasonography).
2. That the information needed affects the care of the patient and fetus during the pregnancy.
3. That the referring physician is of the opinion that it is not prudent to wait to obtain this information until after the patient is no longer pregnant.
B. It is recommended that pregnant patients undergoing a diagnostic imaging examination with ionizing radiation and iodinated contrast media provide informed consent to document that they understand the risk and benefits of the procedure to be performed and the alternative diagnostic options available to them (if any), and that they wish to proceed.
Gadolinium-Based Contrast Agents
It is known that gadolinium-based MR contrast media cross the human placenta and into the fetus when given in clinical dose ranges. No adequate and well-controlled teratogenic studies of the effects of these media in pregnant women have been performed. A single cohort study of 26 women exposed to gadolinium chelates during the first trimester of pregnancy showed no evidence of teratogenesis or mutagenesis in their progeny.
Gadolinium chelates may accumulate in the amniotic fluid and remain there for an indefinite period of time, with potential dissociation of the toxic free gadolinium ion from the chelate; the significance of this exposure to the fetus is uncertain, and its potential association with nephrogenic systemic fibrosis (NSF) in the child or mother is unknown. Therefore, gadolinium chelates should not be routinely used in pregnant patients.
The ACR Guidance Document for Safe MR Practices also covers use of MR contrast media in pregnant patients, and its recommendations are consistent with those in this Manual. See also the preceding Chapter on NSF (www.acr.org/SecondaryMainMenuCategories/quality_safety/contrast_manual/NephrogenicSystemicFibrosis.aspx)
Because it is unclear how gadolinium-based contrast agents will affect the fetus, these agents should be administered only with extreme caution. Each case should be reviewed carefully and gadolinium-based contrast agent administered only when there is a potential overwhelming benefit to the patient or fetus that outweighs the possible risk of exposure of the fetus to free gadolinium ions. The radiologist should confer with the referring physician and document the following in the radiology report or the patient’s medical record:
1. That information requested from the MR study cannot be acquired without the use of IV contrast or by using other imaging modalities.
2. That the information needed affects the care of the patient and fetus during the pregnancy.
3. That the referring physician is of the opinion that it is not prudent to wait to obtain this information until after the patient is no longer pregnant.
It is recommended that the pregnant patient undergoing an MR examination provide informed consent to document that she understands the risk and benefits of the MR procedure to be performed, and the alternative diagnostic options available to her (if any), and that she wishes to proceed.
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