Ultrasound and MRI don't use ionising radiation and are the preferred scans in pregnancy. X-ray, CT and nuclear medicine do use radiation and are generally avoided unless the information is important — though a single scan is considered low-risk, especially away from the abdomen. Gadolinium contrast is usually avoided; iodine contrast isn't known to pose significant risk to the baby. Always tell staff you are, or might be, pregnant.
Key takeaways
- Ultrasound and MRI are first-choice because they use no ionising radiation.
- A single X-ray or CT is generally low-risk; doctors weigh benefit against a very small risk.
- Gadolinium contrast is usually avoided; iodine contrast isn't known to harm the baby.
- Tell every clinician you are, or might be, pregnant before any scan.
If you’re pregnant and your doctor recommends a scan, it’s natural to worry. The reassuring news: the scans used most often in pregnancy use no ionising radiation at all, and even the ones that do are used carefully and only when the information matters for your care.
The radiation-free scans come first
Ultrasound is the mainstay of pregnancy imaging — it uses sound waves, has no known adverse effects, and is used routinely to monitor the baby.[2] MRI also uses no ionising radiation. It is not contraindicated in pregnancy, and no harm to the baby has been documented — but scanning in the first trimester is generally kept for when it’s needed and discussed with the radiologist.[3]
X-ray, CT and nuclear medicine
These use ionising radiation, so they’re generally avoided in pregnancy. When they’re genuinely needed, they’re still used — a single diagnostic X-ray or CT is considered low-risk, and your doctor weighs that small risk against the importance of the diagnosis.[2] A common example is a scan to check for a blood clot on the lung, where the small dose is far outweighed by the danger of missing the clot; the dose is reduced where possible.
What about contrast?
- Gadolinium (MRI contrast) is usually avoided in pregnancy because the risk to the baby isn’t fully known.[1]
- Iodine contrast (CT) is not known to pose any significant risk to mother or baby, though there’s a small theoretical chance it can affect the newborn’s thyroid — one reason all babies born in Australia have routine newborn thyroid screening anyway.[1] If you’re breastfeeding, you don’t need to stop or discard milk after iodine or gadolinium contrast.[1]
What to tell your care team
Always mention that you are, or might be, pregnant — when booking and again on the day. It lets the team choose the safest test, adjust technique, and decide whether contrast or a tracer is appropriate.[2]
Frequently asked questions
Is an ultrasound safe during pregnancy?
Yes — ultrasound uses sound waves, not radiation, has no known adverse effects, and is the standard scan used to monitor pregnancy.[2]
Can I have an MRI while pregnant?
MRI is not contraindicated in pregnancy and no harm to the baby has been shown, but it’s used when needed rather than routinely in the first trimester, and gadolinium contrast is usually not given.[3]
I had a scan before I knew I was pregnant — should I worry?
Almost always, no. Ultrasound and MRI carry no radiation risk, and a single X-ray or CT — especially away from the abdomen — is low-risk. Tell your doctor, who can reassure you with the specifics.[2]
Sources
- RadiologyInfo.org (RSNA & ACR) — Contrast Materials (pregnancy) — www.radiologyinfo.org/en/info/safety-contrast
- RANZCR / InsideRadiology — Radiation risk of medical imaging — www.insideradiology.com.au/radiation-risk/
- RANZCR / InsideRadiology — Magnetic resonance imaging (MRI) — www.insideradiology.com.au/mri-hp/
