What are the guidelines for using Magnetic Resonance Imaging (MRI) during pregnancy?

MRI Guidelines in Pregnancy

MRI without contrast is safe during pregnancy and can be performed when medically necessary, while gadolinium-based contrast agents should be avoided unless absolutely essential and benefits clearly outweigh risks.

Safety of Non-Contrast MRI During Pregnancy

• MRI is considered safe for pregnant patients as it uses non-ionizing radiation with no known adverse effects on human fetuses when performed using standard 1.5T or 3.0T magnets 1
• Multiple guidelines recommend MRI as the preferred second-line imaging modality after ultrasound during pregnancy 2, 1
• A large retrospective study of 1,737 pregnancies with first-trimester MRI exposure found no increased risk of congenital anomalies, neoplasms, or vision or hearing loss compared to unexposed pregnancies 3

Timing of MRI During Pregnancy

• While MRI can be performed at any trimester when medically necessary, the American College of Radiology recommends:
  • Optimal timing for diagnostic quality MRI is after 24 weeks gestation 1
  • MRI between 18-22 weeks may be valuable for certain clinical indications 2

Gadolinium-Based Contrast Agents (GBCAs)

• GBCAs should be avoided during pregnancy unless absolutely essential 2, 1, 4
• The FDA label for gadolinium states: "Use Gadoteridol Injection only if imaging is essential during pregnancy and cannot be delayed" 4
• Concerns with gadolinium use during pregnancy include:
  • GBCAs cross the placental barrier and result in fetal exposure and gadolinium retention 4
  • Gadolinium is excreted into amniotic fluid and may remain there for an indeterminate time 2
  • A large retrospective study found gadolinium exposure during pregnancy was associated with:
    • Increased risk of rheumatological, inflammatory, or infiltrative skin conditions (adjusted HR 1.36) 3
    • Higher risk of stillbirth or neonatal death (adjusted RR 3.70) 3

Practical Guidelines for MRI During Pregnancy

1. First-line imaging: Always consider ultrasound as the first imaging modality during pregnancy 2, 1

2. When MRI is needed:

   • Perform non-contrast MRI when ultrasound is inconclusive or insufficient 2, 1
   • Position patient in left lateral or left pelvic tilt position to avoid inferior vena cava compression 2, 1
   • Use the "as low as reasonably achievable" principle to minimize exposure time 2

3. Contrast considerations:

   • If contrast is deemed necessary, document the rationale thoroughly 2
   • Obtain informed consent after discussion with the referring physician 2
   • Consider the specific clinical scenario and whether the information could be obtained without contrast 2, 4

Special Clinical Scenarios

• Neurological conditions: Non-contrast MRI is preferred over CT for neurological assessment during pregnancy due to lack of ionizing radiation 5

• Oncologic imaging: Whole-body diffusion-weighted MRI (WB-DWI/MRI) can be used as a single-step staging modality for cancer in pregnancy, avoiding the need for PET/CT 2

• Inflammatory bowel disease: Non-contrast MRI has been used successfully to evaluate active Crohn's disease and complications during pregnancy 2

• Fetal anomalies: Fetal MRI is indicated following an ultrasound examination when information about fetal abnormalities is incomplete, ideally performed at or after 22 weeks gestation 2

Important Precautions

• Always document the medical necessity of MRI during pregnancy
• If sedation is required, use the lowest effective dose of safer options like meperidine or fentanyl 1
• Avoid benzodiazepines when possible, especially in the first trimester 1
• For patients requiring regular MRI monitoring (e.g., cancer patients), consider timing studies to minimize fetal exposure while maintaining adequate maternal care

Remember that while MRI is generally considered safe during pregnancy, each case should be evaluated based on the clinical urgency, potential benefit to the mother and fetus, and availability of alternative imaging options.