MRI is considered safe during pregnancy. Both the American College of Obstetricians and Gynecologists (ACOG) and the American College of Radiology state that MRI is not associated with risk to the fetus and is, along with ultrasound, the preferred imaging method for pregnant patients. That said, MRI is still used selectively during pregnancy, reserved for situations where it will genuinely answer a clinical question or change how you’re treated.
What the Evidence Shows About Fetal Safety
MRI uses strong magnetic fields and radio waves to create images of the body. Unlike X-rays or CT scans, it produces no ionizing radiation, which is the type of radiation linked to birth defects and developmental harm. The main theoretical concerns with MRI during pregnancy have centered on three things: tissue heating, loud noise exposure, and potential effects on early fetal development.
Large studies have addressed each of these. A study tracking 1,737 fetuses exposed to MRI during the first trimester compared outcomes against nearly 1.42 million unexposed fetuses. At a four-year follow-up, there was no significant increase in stillbirth, congenital anomalies, cancer, vision loss, or hearing loss in the MRI-exposed group. Another study compared hearing screening results in 751 newborns who had been exposed to MRI before birth with over 10,000 unexposed newborns. The rate of hearing impairment was 0% in the exposed group, compared to 0.34% in the unexposed group.
Multiple additional studies examining babies scanned during the second and third trimesters have found no adverse effects on hearing, birth weight, or newborn health scores. Children who underwent prenatal MRI have also passed hearing tests at preschool age with no issues, and the total duration of the scan did not correlate with any negative outcomes.
First Trimester Safety
Many people worry specifically about MRI during the first trimester, when organs are forming and the fetus is most vulnerable to outside influences. Some animal studies have shown associations between prolonged MRI exposure and skeletal changes or weight differences, but these involved exposure times far beyond what happens in a clinical scan.
In humans, the American College of Radiology has reviewed the available data and concluded that no special precautions are needed for the first trimester compared to any other point in pregnancy. The large study of over 1,700 first-trimester exposures supports this position, finding no meaningful increase in birth defects or other complications. One narrow finding worth noting: when MRI exposure was restricted to between 5 and 10 weeks of gestation, researchers observed a small increase in the risk of vision loss (roughly double the baseline rate), though no other studies have replicated this finding.
Noise and Heating During the Scan
MRI machines are loud. The banging and buzzing sounds come from rapid electrical changes in the scanner’s internal coils, and noise levels can reach well above 100 decibels. For the fetus, though, amniotic fluid and maternal tissue act as a buffer. Studies tracking newborn hearing after prenatal MRI at both 1.5 Tesla and 3 Tesla scanners (the two standard strengths) have consistently found no hearing damage. Fail rates on newborn hearing tests showed no significant difference between the two scanner strengths.
Tissue heating is the other physical concern. MRI deposits radiofrequency energy into the body, and international safety guidelines cap the whole-body energy absorption at 2 watts per kilogram for pregnant patients, which is the standard “normal operating mode.” The heating effect is strongest near the scanner’s surface and drops off significantly by the time it reaches the uterus. While computer simulations have modeled scenarios where fetal temperatures could theoretically rise, clinical studies at recommended power levels have not shown harmful heating in practice.
1.5T Versus 3T Scanners
Most prenatal MRI is done on 1.5 Tesla machines, which remain the standard recommendation. However, 3 Tesla scanners are increasingly used and have been studied in pregnancy. The higher-strength scanner produces sharper images with better contrast, which can be clinically useful when examining fetal brain structures or other fine anatomy.
Interestingly, one study found that with appropriate adjustments to the scanning technique, 3T MRI actually deposited less radiofrequency energy than 1.5T (an average of 0.6 versus 1.6 watts per kilogram), while producing higher image quality. Images from the 3T scanner showed equal or better tissue contrast in over 90% of cases. Both scanner strengths produced diagnostic-quality images, and neither was associated with adverse hearing outcomes in newborns.
The One Real Concern: Contrast Dye
Where the safety picture changes is with gadolinium, a contrast agent sometimes injected during MRI to make certain tissues show up more clearly. Gadolinium crosses the placenta and enters fetal circulation, and the fetus swallows it with amniotic fluid. Unlike the MRI scan itself, gadolinium has raised legitimate safety signals.
One study found a small increased risk of stillbirth and neonatal death following gadolinium exposure during pregnancy. The same research group observed higher rates of inflammatory and skin conditions in young children who were exposed to gadolinium during the first trimester. A separate analysis of 397 pregnancies exposed to gadolinium around conception found no increase in major birth defects, but did confirm the small uptick in stillbirth or neonatal death.
Because of these findings, ACOG recommends that gadolinium contrast should only be used during pregnancy when it will significantly improve the accuracy of the diagnosis and is expected to change the outcome for the mother or baby. In most cases, MRI during pregnancy is performed without contrast. If you’re breastfeeding, gadolinium is not a concern: only a tiny fraction passes into breast milk, and ACOG says there is no need to interrupt breastfeeding after receiving it.
When Prenatal MRI Is Recommended
MRI during pregnancy is not routine. It is typically ordered when ultrasound cannot fully answer a diagnostic question. The most common reasons include suspected brain or spinal cord abnormalities in the fetus, masses in the neck or throat that could affect delivery, diaphragmatic hernia (where abdominal organs push into the chest cavity), abdominal masses, bowel problems not fully visible on ultrasound, and suspected fetal infection.
For the mother, MRI may be needed to evaluate conditions like appendicitis, ovarian masses, or neurological symptoms where a CT scan’s radiation would be best avoided. In these situations, MRI provides detailed imaging without exposing either you or the fetus to ionizing radiation, making it the safest advanced imaging option available.