Is It Safe for You and Your Baby to Have an MRI During Pregnancy?

Imaging studies like x-rays, MRI, ultrasound, and computed tomography (CT) scans have become a common and valuable part of medical diagnosis. In most cases they are considered routine and essential for diagnosing common problems for everything from trauma to tumors. But, when you become pregnant, most people – even doctors – assume that imaging studies are off limits.

The truth is, many imaging studies are safe in pregnancy and could be used more often than they are. According to the American College of Obstetricians and Gynecologists (ACOG), confusion about the risks from imaging studies often results in unnecessary avoidance.

The major fear from imaging studies is radiation exposure to an unborn child. The risk of exposure depends on the amount of radiation and the age of the fetus. Radiation is three times more dangerous in the first trimester than in the last trimester. Fear is understandable when you consider the known risks to a developing baby, which include growth restriction, microcephaly, birth defects, intellectual disability, and cancer.

Ultrasound imaging using sound waves is considered the safest imaging procedure during pregnancy. There is no exposure to radiation, and ultrasound does a good job diagnosing common problems that may occur during pregnancy, like appendicitis or gall bladder disease. Plain x-rays, CT, and nuclear medicine imaging all involve some radiation exposure. These imaging studies may still be used in certain situations, if the benefit of diagnosis and treatment clearly outweighs the risk.

The truth is, many imaging studies are safe in pregnancy and could be used more often than they are. According to the American College of Obstetricians and Gynecologists (ACOG), confusion about the risks from imaging studies often results in unnecessary avoidance.

What About MRI?

As your pregnancy advances and your uterus increase in size, the ability of ultrasound to give an accurate diagnosis may decrease. Like ultrasound, MRI does not use radiation to create images. MRI uses magnets in place of radiation. MRI provides excellent imaging of soft tissues deep inside the body.

The concerns about MRI use in pregnancy have to do with the effects of magnetic field on a developing baby and the exposure to the baby’s developing hearing system from the noise of the MRI. Although theoretically these could be harmful, there has never been any evidence that they actually cause any harm.

After reviewing all the available evidence, the American College of Radiology concluded that MRI was safe during all trimesters of pregnancy.  The American Academy of Pediatrics says that MRI is safe for a baby’s hearing as long as the decibel level of the MRI is below 91 decibels. Studies show that sound does not reach this level inside the womb. The National Radiological Protection Board advises against using MRI in the first trimester. However, recent studies do not find any fetal harm from first trimester MRI, so this is still a bit of a gray area. Ultrasound would still be the first choice, but MRI can be considered if needed.

One area that is less gray is the use of contrast dyes during MRI. MRI creates good images even without contrast, but adding an intravenous dye before imaging is often done to get better images of the brain and spinal cord. The most common dye is called gadolinium, and it is not considered safe to use in pregnancy. Gadolinium can cross from the blood stream through the placenta and into amniotic fluid. There is some evidence that gadolinium can increase the risk of muscle and joint disease, inflammation, skin conditions, and stillbirth. For these reasons the use of MRI with gadolinium is avoided.

ACOG guidelines say that if you have a gadolinium MRI scan after giving birth, the gadolinium does not cross significantly into breast milk, and breastfeeding should not be interrupted.

What If You Need an Imaging Study with Radiation Exposure?

There are cases where the benefit of having a plain x-ray film, CT scan, or even a nuclear medicine scan outweighs the risk of radiation exposure. ACOG guidelines say that with few exceptions, the radiation exposure from these types of imaging studies is much lower than the amount of exposure known to cause damage to your baby.

For example, evidence suggests that the minimum amount of radiation required to cause fetal harm is around 50 to 60 milligray (mGy). A chest x-ray only exposes a fetus to 0.002 mGy. An abdominal CT scan exposes your baby to 4 mGy. Nuclear medicine imaging exposes your baby to about 5 mGy, all well below the danger limit.

Christopher Iliades
Dr. Chris Iliades is a medical doctor with 20 years of experience in clinical medicine and clinical research. Chris has been a full time medical writer and journalist since 2004. His byline appears in over 1,000 articles online including EverydayHealth, The Clinical Advisor, and Healthgrades. He has also written for print media including Cruising World Magazine, MD News, and The Johns Hopkins Children's Center Magazine. Chris lives with his wife and close to his three children and four grandchildren in the Boston area.

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