MRI Safety and Clinical Use in Pregnancy

Safety of Non‑Contrast MRI

• The American College of Radiology states that non‑contrast MRI is safe at any gestational age and may be performed without hesitation when clinically indicated. 1
• MRI without contrast performed on 1.5‑Tesla or 3.0‑Tesla systems shows no known deleterious fetal effects in any trimester. 2
• MRI involves no ionizing radiation, making it superior to CT for fetal evaluation. 3

Indications for MRI When Ultrasound Is Inadequate

• MRI is the preferred second‑line imaging modality when ultrasound is inadequate or inconclusive. 4
• Lesions larger than 10 cm that exceed the ultrasound field of view should be evaluated with MRI. 1
• Poor acoustic windows caused by maternal habitus or adjacent viscera warrant MRI assessment. 4
• Indeterminate pelvic masses benefit from MRI to clarify the organ of origin. 1
• Posterior placentation where ultrasound is limited is best assessed with MRI. 2
• Suspected placenta accreta spectrum disorder after 24 weeks gestation should be investigated with MRI. 2

Contraindication: Gadolinium‑Based Contrast

• Gadolinium‑based contrast agents should not be routinely administered during pregnancy and should be avoided unless the anticipated benefit far outweighs the risk in life‑threatening situations. 5
• Gadolinium crosses the placenta, accumulates in amniotic fluid and fetal tissues, posing potential toxicity. 5
• Prenatal gadolinium exposure is associated with an increased risk of stillbirth or neonatal death (17.6 / 1,000 exposed vs 6.9 / 1,000 unexposed). 1
• Children exposed in utero to gadolinium have a higher incidence of rheumatologic, inflammatory, or infiltrative skin conditions. 3
• The FDA classifies gadolinium as Category C (adverse effects in animal studies; inadequate human data). 4

Timing Considerations

• After 24 weeks gestation is the optimal window for diagnostic‑quality MRI of placental abnormalities. 2

Diagnostic Performance of Non‑Contrast MRI

• Non‑contrast MRI in pregnancy achieves high diagnostic performance (sensitivity ≈ 85 %, specificity ≈ 96 %, overall accuracy ≈ 94 %). 3

Advanced Sequences: Diffusion‑Weighted Imaging (DWI)

• DWI is valuable during pregnancy, enhancing detection of inflammation, abscesses, and tumors without gadolinium. It can differentiate decidualized endometriomas from ovarian cancer and identify solid components in adnexal masses. 1

Clinical Decision Algorithm (American College of Radiology)

• Step 1: Begin with ultrasound as the first‑line imaging modality. 1
• Step 2: If ultrasound is inadequate, proceed directly to non‑contrast MRI. 1
• Step 3: Add DWI sequences to improve diagnostic accuracy without contrast. — (no additional citation needed as DWI benefit already cited)
• Step 4: Reserve gadolinium contrast only for life‑threatening maternal conditions where diagnosis cannot be made otherwise and immediate management depends on contrast‑enhanced imaging. 2

Safety of MRI During Pregnancy

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, according to the American College of Radiology 6, 7, 8.
• 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, as stated by the American College of Radiology 6, 9.
• 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, as reported by the American College of Radiology 10.

Gadolinium Contrast Considerations

• Gadolinium-based contrast agents should be avoided during pregnancy whenever possible, according to the American College of Radiology and the Annals of Oncology 7, 11.
• Gadolinium crosses the placenta and enters the fetal circulation, where it can accumulate in the amniotic fluid and fetal tissues, as found by the American College of Radiology 12.
• 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, as reported by the Annals of Oncology 11.

Clinical Applications of MRI During Pregnancy

• MRI may be helpful as a problem-solving tool for non-tubal ectopic pregnancies, gestational trophoblastic disease, unusual implantation sites, women with uterine anomalies, and placental abnormalities, as stated by the American College of Radiology 6, 9, 10.

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, as recommended by Gastroenterology 13, 14.
• Most procedures should be performed with the patient in a left pelvic tilt or left lateral position to avoid vascular compression, as suggested by Gastroenterology 13, 14.

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, as recommended by the American College of Radiology 10.
• Ultrasound remains the first-line imaging modality for most conditions during pregnancy, with MRI serving as a complementary or problem-solving tool, as stated by the American College of Radiology 6, 9, 15.

Guidelines for Use of Gadolinium Contrast in Pregnancy

General Recommendations

• The American College of Radiology recommends that gadolinium‑based contrast agents should not be administered routinely to pregnant patients and should be avoided unless the imaging is essential for a life‑threatening maternal condition that cannot be diagnosed by other means. 16, 17

• The American College of Radiology advises against the routine ordering of contrast‑enhanced MRI in pregnancy simply because it is standard practice in non‑pregnant patients. 16

Risks Associated with Gadolinium

• The American College of Radiology notes that gadolinium crosses the placenta and accumulates in amniotic fluid and fetal tissues, creating potential toxicity with an unknown duration of fetal exposure. 16

• The American College of Radiology reports that prenatal gadolinium exposure is linked to stillbirth or neonatal death at a rate of 17.6 per 1,000 exposed fetuses versus 6.9 per 1,000 unexposed fetuses. 16

• The American College of Radiology indicates that children exposed in utero to gadolinium have a higher incidence of rheumatologic, inflammatory, or infiltrative skin conditions. 16

• The American College of Radiology classifies gadolinium‑based contrast agents as FDA Category C drugs, meaning adverse effects have been demonstrated in animal studies but human data are insufficient. 16

Situations Where Gadolinium May Be Considered (Rare Exceptions)

• The American College of Radiology states that gadolinium may be considered only when the imaging is essential, cannot be delayed or replaced by alternative modalities, and the anticipated clinical benefit far outweighs the unknown fetal risk. 18

• The American College of Radiology emphasizes that the indication must be critical, with potential benefits substantially outweighing the potential unknown risk to the fetus. 19

• The American College of Radiology cites a study of pregnant patients with adnexal masses in which 7 of 31 patients who received gadolinium all had malignant tumors on final pathology, illustrating a scenario where contrast aided definitive diagnosis. 16

Diagnostic Performance of Non‑Contrast MRI (Supporting the Preference for Non‑Contrast Imaging)

• The American College of Radiology reports that non‑contrast MRI provides a sensitivity of approximately 85 % and specificity of 96 % for identifying malignancy in adnexal masses. 17