MRI Scan During Pregnancy: Is It Safe?

If you're pregnant and need an MRI scan, it's natural to worry about the safety for you and your baby. The reassuring headline: MRI is generally considered safe during pregnancy because it uses no ionising radiation. But there are some important nuances. This guide gives you the evidence-based picture.

Is MRI Safe During Pregnancy?

MRI uses magnetic fields and radio waves — not X-rays. This is a fundamental distinction. Ionising radiation (X-rays, CT) can damage developing cells and carries known risks during pregnancy. MRI avoids this entirely.

The Royal College of Radiologists, the American College of Radiology, and the European Society of Radiology all confirm that MRI can be performed at any stage of pregnancy when the clinical benefit justifies it. There is no published evidence that clinical MRI has ever caused harm to a human foetus.

That said, caution is applied — particularly regarding timing and contrast.

When Might You Need an MRI During Pregnancy?

• Acute abdominal pain — Investigating appendicitis, bowel obstruction, or ovarian torsion when ultrasound is inconclusive. MRI is the preferred second-line investigation (rather than CT) because it avoids radiation.
• Neurological symptoms — Severe headaches, seizures, visual disturbances, or suspected stroke or cerebral venous sinus thrombosis.
• Foetal assessment — When ultrasound findings are unclear, foetal MRI provides detailed images of the baby's brain, spine, lungs, and other structures. It's particularly useful for brain malformations, lung volume assessment, and complex congenital anomalies.
• Pelvic or spinal conditions — Disc herniations (which can worsen during pregnancy), pelvic masses, or sacroiliac joint problems.
• Cancer staging — If cancer is diagnosed during pregnancy, MRI helps with staging without radiation exposure.
• Placental assessment — Placenta accreta spectrum (where the placenta grows too deeply into the uterine wall) can be assessed with MRI when ultrasound is inconclusive.

Trimester-Specific Guidance

First Trimester (Weeks 1-12)

MRI is generally avoided during the first trimester as a precaution — not because of proven risk. This is the period of organogenesis, when major organs are forming. The precautionary principle suggests minimising any unnecessary exposure during this sensitive window.

However, if MRI is clinically urgent during the first trimester (for example, suspected appendicitis or stroke), it can and should be performed. The risk of missing a dangerous diagnosis far outweighs any theoretical concern about the MRI itself.

Some animal studies have shown effects on embryonic development at very high magnetic field strengths (above those used clinically), but these findings have not been replicated in humans, and large human cohort studies (Ray et al., JAMA 2016, studying over 1.4 million pregnancies) found no increased risk of adverse outcomes from MRI during pregnancy, including first trimester exposure.

Second and Third Trimesters (Weeks 13-40)

MRI is considered safe and is performed routinely when clinically indicated. Foetal MRI (dedicated imaging of the baby) is typically performed from 18-20 weeks onwards, when the foetus is large enough for meaningful assessment.

Gadolinium Contrast During Pregnancy

Gadolinium contrast is generally avoided during pregnancy. Key concerns:

• Gadolinium crosses the placenta into the foetal circulation
• It is excreted by the foetal kidneys into the amniotic fluid, where the foetus swallows it, creating a recirculation loop
• Free gadolinium (released from its chelate complex) is toxic, and the duration of exposure in the foetal compartment is uncertain
• A large retrospective study (Ray et al., JAMA 2016) found a possible association between first-trimester gadolinium exposure and rheumatological, inflammatory, and skin conditions in childhood, though the absolute risk was small and the evidence was observational

Current guidelines: avoid gadolinium during pregnancy unless the information it provides is essential and cannot be obtained any other way. Most pregnancy-related MRI scans can be performed adequately without contrast.

Practical Considerations

Positioning

In late pregnancy, lying flat on your back for 30-60 minutes can cause discomfort and supine hypotension (the weight of the uterus compresses the inferior vena cava, reducing blood flow back to the heart). You may be positioned with a slight left lateral tilt using foam wedges, or the scan may be broken into shorter segments with rest breaks.

Noise

MRI scanners are loud (80-100+ dB). The foetus can hear external sounds from roughly 18 weeks onwards. While there's no evidence that MRI noise causes foetal hearing damage (the amniotic fluid and maternal tissues attenuate the sound), ear protection is provided to the mother, and exposure is kept as short as reasonably possible.

Heating (SAR)

Radiofrequency energy can cause mild tissue heating, measured as Specific Absorption Rate (SAR). During pregnancy, SAR limits are monitored carefully to keep within recommended levels. There is no evidence that clinical SAR levels cause foetal harm.

Breastfeeding After MRI

MRI itself has no effect on breast milk. You can breastfeed immediately after a non-contrast MRI.

If gadolinium contrast is used, current guidelines (ESUR, ACR) confirm that breastfeeding can continue without interruption. Less than 0.04% of the injected gadolinium dose passes into breast milk, and less than 1% of that is absorbed through the infant's gut. The risk to the baby is negligible. Some mothers choose to express and discard milk for 24 hours out of caution — this is a personal choice, not a medical requirement.

Frequently Asked Questions

Can MRI cause a miscarriage?

There is no evidence that MRI causes miscarriage. Large population studies (including the Ray et al. 2016 JAMA study of over 1.4 million pregnancies) found no increased risk of stillbirth, neonatal death, congenital malformations, hearing loss, or vision loss associated with MRI during pregnancy.

Is MRI safer than CT during pregnancy?

Yes, generally. MRI avoids ionising radiation entirely, making it the preferred imaging choice during pregnancy when ultrasound is insufficient. CT is used during pregnancy only when the clinical urgency is high and MRI isn't practical (e.g., suspected pulmonary embolism, where CT pulmonary angiography remains the fastest diagnostic test).

Can I have an MRI to check on my baby?

Yes. Foetal MRI is an established clinical tool, typically performed from 18-20 weeks onwards. It provides detailed information about the baby's brain, spine, lungs, and other structures when ultrasound findings need clarification. Foetal MRI is usually arranged through your obstetrician or maternal-foetal medicine specialist.

Should I tell the scanning team I'm pregnant?

Absolutely. Always inform the scanning team if you're pregnant or think you might be, even if you're only a few weeks along. The team will tailor the scan protocol to minimise exposure time and SAR, and they'll avoid contrast unless it's medically necessary.

Can I have an MRI if I'm trying to conceive?

Yes. There is no evidence that MRI affects fertility or early conception. If you're in the earliest stages of pregnancy (before you know), the exposure from a single MRI is not considered a risk.