Is it safe to have an MRI (Magnetic Resonance Imaging) during pregnancy?

Safety of MRI During Pregnancy

MRI without gadolinium contrast is considered safe during pregnancy and can be performed when medically necessary.

General Safety of MRI in Pregnancy

• MRI does not use ionizing radiation, making it a preferred imaging modality over CT for pregnant women when ultrasound is inadequate 1.
• Non-contrast MRI is thought to be safe in all trimesters of pregnancy, as no evidence of adverse fetal effects has been demonstrated to date 1, 2.
• While MRI safety has not been definitively established with regard to static magnetic field exposure, tissue heating effects from radio-frequency pulses, and high acoustic noise levels, no harmful effects have been documented 1.
• Pregnant patients can be informed that there are no known deleterious effects on the fetus when MRI is performed in 1.5T or 3.0T magnets 1.

Gadolinium Contrast Considerations

• Gadolinium-based contrast agents should be avoided during pregnancy whenever possible 1, 3.
• Gadolinium crosses the placenta and enters the fetal circulation, where it can accumulate in the amniotic fluid and fetal tissues 1, 3.
• A recent study found that gadolinium exposure during pregnancy was associated with increased risk of rheumatologic, inflammatory, or infiltrative skin conditions in offspring and increased risk of stillbirth or neonatal death 1.
• Gadolinium should only be used when critical and the potential benefits are felt to justify the risks 1, 4.
• Gadolinium is considered a pregnancy category C drug (it should be administered only if the potential benefit outweighs the risk) 1.

Clinical Applications of MRI During Pregnancy

• MRI is rarely needed for evaluating intrauterine pregnancy or tubal pregnancy, as ultrasound is typically sufficient 1.
• MRI may be helpful as a problem-solving tool for:
  • Non-tubal ectopic pregnancies 1
  • Gestational trophoblastic disease 1
  • Unusual implantation sites 1
  • Women with uterine anomalies 1
  • Neurological conditions 2
  • Acute abdominal and pelvic pain when ultrasound is inconclusive 1, 5
  • Placental abnormalities 1, 5

Practical Considerations

• When performing MRI on pregnant patients:
  • Avoid positioning patients on their backs as the pregnant uterus can compress the aorta or inferior vena cava, resulting in maternal hypotension and decreased placental perfusion 1.
  • Most procedures should be performed with the patient in a left pelvic tilt or left lateral position to avoid vascular compression 1.
  • Whole-body diffusion-weighted MRI (WB-DWI/MRI) can be used for staging and tumor response evaluation in pregnant women with cancer 1.

Common Pitfalls and Caveats

• The earliest recommended timing for a diagnostic quality MRI scan for placenta accreta spectrum disorder after a suspicious ultrasound is after 24 weeks of gestation 1.
• Ultrasound remains the first-line imaging modality for most conditions during pregnancy, with MRI serving as a complementary or problem-solving tool 1.
• The risk-to-benefit ratio varies from patient to patient depending on many factors, including gestational age and clinical urgency 1.
• Newer MRI scanners use stronger magnets, leading to increased fetal exposure to magnetic fields, and research is mostly based on older MRI data 1.

In conclusion, non-contrast MRI is considered safe during pregnancy when medically necessary, but gadolinium contrast should be avoided unless the benefits clearly outweigh the potential risks to the fetus.