Is iodine (I) contrast during Magnetic Resonance Imaging (MRI) dangerous for pregnant women?

MRI Contrast Safety During Pregnancy

Iodinated contrast is not used in MRI scans, and gadolinium-based contrast agents should be avoided during pregnancy due to potential risks to the fetus. 1, 2

Understanding Contrast Agents in MRI

MRI uses gadolinium-based contrast agents (GBCAs), not iodine-based contrast. This is a common misconception that needs clarification:

• MRI uses gadolinium-based contrast agents
• CT scans use iodinated contrast agents

Gadolinium Contrast Risks During Pregnancy

Gadolinium-based contrast agents are contraindicated during pregnancy for several important reasons:

• Gadolinium crosses the placenta and enters fetal circulation 1, 2
• A 2016 study showed increased risk of stillbirth or neonatal death (17.6/1,000 in exposed fetuses versus 6.9/1,000 in unexposed fetuses) 1
• Increased risk of childhood rheumatological, inflammatory, or infiltrative skin conditions 1
• FDA categorizes gadolinium-based contrast agents as category C drugs (adverse effects in animal studies without adequate human studies) 1

Recommended Imaging Approach During Pregnancy

First-line Imaging

• Ultrasound without contrast is the preferred first-line imaging modality throughout pregnancy 1, 2
• Safe and non-ionizing with high strength of evidence (8/9) 2

Second-line Imaging

• MRI without contrast when ultrasound is inconclusive 1, 2
• Non-contrast MRI is considered safe during pregnancy 2
• Non-contrast MRI can achieve high diagnostic accuracy (sensitivity 85%, specificity 96%) 1

When Contrast Is Absolutely Necessary

• Use of gadolinium should be restricted to situations where potential benefits far outweigh risks to the fetus 1
• A multidisciplinary approach involving radiologists, obstetricians, and specialists is recommended for these rare cases 1

Important Clinical Considerations

• Inadvertent exposure to GBCAs often occurs in early pregnancy before recognition 3
• 70.2% of GBCA exposures during pregnancy occur in the first trimester 3
• If MRI with contrast was performed before pregnancy was known, careful monitoring is recommended but termination is not indicated based on exposure alone 4

Common Pitfalls to Avoid

1. Confusing contrast types: Iodinated contrast is used for CT scans, not MRI
2. Assuming all contrast is equally risky: Gadolinium has specific concerns during pregnancy
3. Delaying necessary imaging: Non-contrast MRI is generally safe and preferred over CT when ultrasound is insufficient
4. Overlooking alternatives: Diffusion-weighted imaging and other non-contrast MRI techniques can often provide adequate diagnostic information 1

For pregnant patients requiring advanced imaging, the evidence-based approach is clear: ultrasound first, non-contrast MRI second, and gadolinium-based contrast only in exceptional circumstances where benefits clearly outweigh risks.