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There are multiple indications for

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performing MRI during pregnancy.

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Some of them are unrelated to the pregnancy

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itself and may include neurological

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indications, and musculoskeletal indications.

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Acute abdominal pain is something

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for which we very frequently

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perform MRI in pregnant patients.

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Common conditions occurring in pregnancy

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for which we would do MRI include

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appendicitis, acute or chronic hepatobiliary

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pathology, and nephrolithiasis.

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We can also use MRI to evaluate obstetric

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abnormalities, and in those cases, MRI

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may be extremely useful for operative

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planning for this patient population.

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MRI is an extremely safe imaging

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modality to use during pregnancy.

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We have decades of data regarding the use

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of MRI in pregnant patients, none of which

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suggests that MRI is harmful to the fetus.

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One of those reasons, of course, is

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because we're using radiofrequency

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pulses within a magnetic field, again,

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instead of ionizing radiation for CT.

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MRI is wonderful because we can get large

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field of view images with excellent tissue

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characterization, and the images are often

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diagnostic without intravenous contrast.

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I want to point out that MRI is safe to perform

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in pregnancy in all three trimesters, both at 1.5

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tesla and 3 tesla.

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There were initially, at the advent of

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MRI, concerns about tissue heating and

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specific absorption rate for the fetus.

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However, we know now that most of the

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tissue heating that occurs in the context

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of MRI really happens at the skin's surface,

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which is maternal tissue, and the

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uterus and fetus are deep to that.

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Additionally, the amniotic fluid

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that's surrounding the fetus continues

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to circulate, so it's dissipating

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any heat that may reach the fetus.

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There is also a theoretical risk to the

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fetal ossicles due to the noise that may

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happen during the exam, particularly in

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the context of gradient echo imaging.

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However, this hasn't really panned out in many

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of the human studies that we've performed.

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We've not seen a lot of babies born with

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hearing-related issues thought to be

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due to noise exposure during the MRI.

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Let's also talk about the use of gadolinium-

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based contrast agents in pregnant patients.

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Gadolinium contrast is water-soluble,

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so it does cross the placenta.

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And because gadolinium is renally excreted, it

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can lead to cyclic re-exposure to the fetus,

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because as the gadolinium crosses the placenta,

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it enters the fetal circulation, is excreted

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by the fetal kidneys, and then is urinated

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out by the fetus into the amniotic fluid.

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Because the fetus also swallows the

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amniotic fluid, there's a continuous

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re-exposure to the gadolinium contrast.

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Because the gadolinium contrast is persisting

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for longer than we would like in the fetal

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circulation and the amniotic fluid, there is the

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potential for that free gadolinium to dissociate

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from the chemical chelate to which it's bound.

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And so there are recent studies that have

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come out showing that fetuses exposed

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to gadolinium-based contrast agents

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are at increased risk of rheumatologic,

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inflammatory, or infiltrative skin conditions.

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Gadolinium-based contrast agents

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are also considered a class C drug

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because some animal studies have

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shown the potential for teratogenesis.

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And so for all of these reasons, there is

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really almost no reason to use gadolinium-

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based contrast in pregnant patients,

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and it is not routinely indicated.