My doctor ordered a fetal MRI: What do I need to know?


fetal MRI is a specialized imaging test that may be helpful in evaluating your fetus for congenital anomalies and associated complications. You may have had an ultrasound which detected an abnormality, or perhaps genetic testing revealed an increased risk for a syndrome. At Texas Children's Pavilion for Women, we perform several fetal MRI exams every week. Here are the things you need to know to prepare for your test:

What is MRI?

MRI stands for Magnetic Resonance Imaging. The technique is not new, but being able to perform MRI on a fetus has only been possible relatively recently, due to technological advances that allow us to obtain images faster than ever before. Obtaining images quickly is important for fetal MRI, since the fetus moves constantly!  MRI works by placing the patient (in this case, you and your fetus) inside a very large magnet, which creates a magnetic field around you. This magnetic field causes all of your water molecules to line up the same way -- don't worry, you won't feel a thing! We then apply smaller magnetic fields in different ways and measure the way your water molecules go back to their normal position, which allows us to create a variety of images.

Is it safe?

Like ultrasound, MRI does not use the type of radiation that can cause DNA damage, so we believe it is safe to perform in pregnancy. But like with all imaging studies, we only perform fetal MRI when the information gained will affect the management of your pregnancy.

How long will it take?

On average, fetal MRI takes between 30-45 minutes to perform. Occasionally the test lasts a little longer if your fetus happens to be very active during the scan -- more on that below.

I'm claustrophobic! There's no way I'm getting in that machine.

During the test, you will lay on your back or on your left side inside the MRI machine. The opening that you lay inside is not very wide, but MRI machines have to be designed this way to give us the clearest images. The magnet itself never moves, and the opening cannot shrink. The only moving part is the table you lay on, which will slide you in and out of the machine.

The MRI technologist will place pillows under you to make you as comfortable as possible, and she will place noise-cancelling headphones over your ears to protect you from the loud noises made by the secondary magnetic fields. You will have the opportunity to select your own Internet radio station. The technologist can also place a cloth over your eyes so that you are not able to see the MR machine. All of these techniques allow women to undergo fetal MRI exams every day, in spite of feeling claustrophobic.

We encourage you to bring your spouse, significant other, family member or close friend with you, because they can sit next to you while you are having your MRI. If you have small children, it's best to make other arrangements for their care on the day of your appointment, or if you choose to bring them, also bring another adult to watch your children during the MRI examination. Children are not allowed into the MRI scanner room.

How should I prepare?

There is no special preparation for fetal MRI. You may eat breakfast the day of the examination -- in fact, we encourage you to eat breakfast, because we want you to be comfortable.

I had surgery years ago which involved implanted metal. Can I still have an MRI?

Many metals interact with the magnetic field created by the MRI machine, some in quite dangerous ways. In the last 30 years, nearly all orthopedic devices have been made from titanium, which is compatible with MRI scanners; however, we must know the manufacturer and name of the device in order for you to have your MRI. You should give this information to the Fetal Center coordinator when they arrange your appointment, and bring any paperwork you have with you on the day of your test.

Cardiac pacemakers are generally not compatible with MRI machines. There are a few other devices that are also not able to be placed in the magnetic field, like medication pumps. Note that anyone who accompanies you into the scanner room is also subject to these restrictions.

Tattoos may contain small metallic particles in the ink, and occasionally these may warm up after a period of time in the magnetic field. Usually this heating does not cause any discomfort, but you are able to communicate with the MRI technologist during the examination if this becomes an issue.

Your MRI technologist will also have you change into a gown prior to your test, in case of any hidden metal in your clothing (like zippers, buttons and embellishments). You will also be required to remove your jewelry and store all your belongings in one of the provided lockers.

You will always have the opportunity to speak with the pediatric radiologist before your fetal MRI, as we always perform a focused ultrasound exam beforehand. We are always happy to answer your questions! For more information on fetal MRI, visit here.