Ultrasonography is a mainstay of the practice of obstetrics. I’ve seen it evolve over the past 25 years – from large machines that produced very grainy pictures to sleek small machines the size of iPads that give you beautiful images. We use ultrasound at all times during pregnancy for myriad reasons: to measure the size of a fetus, evaluate how much fluid is around a fetus, check the length of a cervix, or look at certain types of fetal activities that are associated with fetal well-being. And, of course, we use it to look at the developing fetus to identify congenital abnormalities.
But sometimes it can be very hard to image a fetus with ultrasound. In certain conditions, like Potter syndrome, amniotic fluid can be absent, making visualization of fetal structures difficult. Later in gestation, the bones of a fetus are more calcified and ultrasound waves don’t penetrate well. So we may detect a potential abnormality, but are unable to get a good enough look with the ultrasound to make a diagnosis. In these cases, we may send you for fetal magnetic resonance imaging (MRI).
We are fortunate to have excellent radiologists at UT Southwestern who work with us in those circumstances. I’ve asked my colleague, Dr. April Bailey, to explain what you can expect if your obstetrician requests a fetal MRI.
How does fetal MRI work?
It’s natural for parents to be nervous when they come in for a fetal MRI. They’re worried about their baby and they may not know how the scan works. The first thing to know about magnetic resonance imaging is that it does not use radiation to capture an image inside the body like an X-ray or CT (computed tomography) scan.
MRI uses a large magnet, pulses of radiofrequency waves, and a computer to create images of your baby. It also does not require intravenous contrast material (dye) or sedation. It is safe for you and safe for your baby.
When you arrive at our office, you’ll be asked to change into a pair of scrubs to help make you more comfortable during the scan. Before starting, we’ll sit down with you so you can ask any questions you may have about the MRI procedure itself. Because metal can interact with the magnetic field produced by the MRI machine, it’s important for you to tell us if you have any medical devices, such as a cardiac pacemaker or orthopedic device.
Next, we’ll ask you to lie on an exam table that slides into a large, tube-shaped machine. There is a microphone in the machine so you can talk to us during the scan, which takes 30 to 40 minutes. It may take a little longer if your baby is moving around a lot. It’s noisy and you may feel warm, but it isn’t noisy or warm inside your body, for your baby.
MRIs can show excellent detail and often are used to get a better look at the baby’s:
- Face and neck
- Chest and lungs
- Abdomen and pelvis (including the bowel, kidneys and bladder)
What happens after the fetal MRI?
The MRI allows us to get a more accurate picture of what your physician saw on the ultrasound. It may show us that there is nothing to be alarmed about. However, if we confirm an abnormality, the images will help your physician better explain the finding and counsel you about the next steps and the care your baby may require.
After the scan, you’ll change back into your own clothing and we’ll sit back down to discuss the results with you. During this discussion, we’ll tell you what the images show and what that may mean. We encourage you to take notes and ask questions. You’ll also receive a disc with the images from the scan.
After this, you’ll go back to your physician for further counseling. They will provide treatment plans as needed for you and your baby. If the MRI does not indicate a problem, or if it’s minor, you may just be able to keep your follow-up appointment with your doctor. If it’s more complicated, we’ll work with your doctor to get you in sooner – the same day, if necessary.
Can any radiologist perform a fetal MRI?
Not all radiologists are trained to interpret a fetal MRI. It’s a specialty that’s not offered at all medical facilities. We perform eight to 10 fetal MRIs a week, and we are tuned in to current fetal imaging literature, which may be different from more general imaging literature.
If there’s a potential problem, most parents want to know about it. You want to know that the person performing your scan understands exactly what it reveals and can explain the results to you. A radiologist trained in fetal MRI can give you the most accurate interpretation of the scan.
Above all, we want to do everything we can to make you comfortable. If you want to bring a loved one with you during the scan and the consultation, please do so. We want to make sure we are providing you with all the information you need to go back to your physician for further counseling on your and your baby’s care.
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