Studies have been limited of low-molecular-weight water-soluble extracellular substances such as gadolinium-based contrast agents used in MR imaging of pregnant patients. Effects on the human embryo or fetus are unknown.

A standard gadolinium-based MRI contrast agent 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 gadolinium-based contrast media behave in a similar fashion and also cross the blood-placental barrier into the fetus.

After entering the fetal bloodstream, these agents are excreted via the urine into the amniotic fluid and 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 a study of primates, placental enhancement could be detected up to two hours following the intravenous administration of gadopentetate dimeglumine. When gadopentetate dimeglumine was injected directly into the amniotic cavity, it was still conspicuous at one hour after administration. There are no data available to assess the rate of clearance of contrast agents from the amniotic fluid.

The American College of Radiology Committee on Drugs and Contrast Media has reviewed this issue extensively and has prepared the following summary of information and recommendations.

GADOLINIUM-BASED MR CONTRAST AGENTS AND PREGNANT WOMEN

It is known that gadolinium-based MRI 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 agents in pregnant women have been performed.

The ACR recommends that all imaging facilities should have policies and procedures to reasonably attempt to identify pregnant patients prior to the performance of the MR exam and before the use of contrast media in these patients. The ACR has issued a White Paper on MR safety in pregnancy and related issues that is consistent with the ACR Committee on Drugs and Contrast Media's recommendation for MRI contrast media.

While there is no compelling evidence of teratogenicity or other adverse effect on the fetus of MR imaging or gadolinium-based contrast agents, neither the safety of the MR environment nor the safety of the contrast agents in pregnant patients has been established. It is therefore prudent for pregnant patients at any stage of pregnancy to be informed of the risk-benefit ratio that may warrant the performance of an MR scan with or without contrast media.

The radiologist should confer with the referring physician and document the following in the radiology report or the patient's medical record:

• The information requested from the MR study cannot be acquired using other nonionizing radiation imaging modalities (e.g., ultrasonography).

• The information needed affects the care of the patient and fetus during the pregnancy.

• 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 with contrast material provide informed consent to document that she understands the risks 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.

[Excerpted with permission from the Runge VM. Chapter 12, Safety of magnetic resonance contrast agents. In: Magnetic resonance procedures: health effects and safety, and the American College of Radiology, Manual on contrast media. Reprinted with permission of the American College of Radiology. No other representation of this article is authorized without express, written permission from the American College of Radiology.]

REFERENCES

American College of Radiology, Manual on contrast media, 5th ed. 2004.

American College of Radiology white paper on MR safety. 2004 update and revisions. AJR 2004;182:111-114.

Panigel M, Wolf G, Zeleznick A. Magnetic resonance imaging of the placenta in rhesus monkeys, Macaca mulatta. J Med Primatol 1988;17:3-18.

Runge VM. Chap 12, Safety of magnetic resonance contrast agents. In: Magnetic resonance procedures: health effects and safety. Boca Raton, FL: CRC Press, 2001:241-260.

Shellock FG, Kanal E. Safety of magnetic resonance imaging contrast agents. J Magn Reson Imaging 1999;10:477-484.