What is a low-dose fetal CT scan?

For a small subset of babies with severely abnormal bones, ultrasound may not provide all the answers. If this is the case, your team of specialized maternal-fetal medicine experts, geneticists and radiologists may suggest a low-dose fetal computed tomography scan (low-dose fetal CT).

A low-dose fetal CT scan offers a three-dimensional view of the fetus that shows the fetal bones in superior detail. This detailed view can help our team reach a final diagnosis.

Many patients feel concerned about the use of fetal CT because of its use of radiation. At CHOP, minimizing radiation exposure to our patients is of utmost importance. In the case of fetal CT scans, our aim is to keep the radiation dose below 5 mSv (unit in which radiation is measured). To put this number in context, a person’s daily exposure to background radiation in Colorado is 3.5 mSv, and a dose up to 50 mSv is thought to be negligible for the fetus.

Low-dose CT scans are only performed in the second and third trimesters of gestation, when fetal organs have already formed and developed, and never during the first trimester, when the fetus is most sensitive to radiation.

If you have any questions or concerns, we encourage you to speak with our team members for more information.

Who you might meet

• Registered CT technologist: highly trained technologist who has specialized in fetal imaging since the inception of CHOP's low-dose fetal CT program in 2008.
• Radiologist: a board-certified, fellowship trained medical doctor who specializes in interpreting imaging studies to diagnose anomalies.

Low-dose fetal CT scan technology

CHOP is a pioneer of low-dose fetal CT in the United States. We use highly advanced CT equipment that minimizes the use of radiation, so that we can provide the best and safest study for you and your fetus.

What to expect

Before starting the exam, the radiologist will explain the low-dose fetal CT scan to you and provide a consent form for you to sign. After the radiologist explains the study and the consent is signed, you will lie down on your back on the CT table. We will place a bolster under your knees to help you feel more comfortable.

The fetal CT study is relatively fast, lasting overall approximately 30 minutes, although the actual scanning time is just a few seconds. The radiologist will stay with you throughout the imaging study.

The CT machine is one large doughnut-like “bore,” with a shorter and wider tube that will feel less closed in than an MRI system. The radiologist will start by doing a very quick ultrasound to mark the top and bottom of the uterus. Once the borders are marked, the CT is done. Capturing the images takes just a few seconds, and you will be ready to move on to your next test.

After completing the scan, the radiologist will examine the images by isolating the fetal bones and reviewing them volumetrically in a 3-D console. The imaging findings will then be discussed with the geneticists and maternal-fetal medicine specialists, who will reach a diagnosis together.

At the end of your day here, our highly trained maternal-fetal specialists will explain to you the findings of the low-dose fetal CT, and of all the studies you have completed during your day with us, and discuss next steps and treatment options.