PET-CT and Pregnancy — Why It Is Not Done

Contact your oncology team and obstetrician as soon as possible. They will arrange a medical physics dose assessment — a calculation of how much radiation the fetus actually received from that specific scan. In many cases the dose is lower than feared. The figure depends on your exact scan, equipment, and gestational age at the time. Do not try to estimate the risk from general information online; your team's dose assessment is the accurate and necessary starting point.

No. The developing brain and nervous system remain sensitive to ionising radiation throughout pregnancy, not only during early organ formation. The scan also directly irradiates the mother's abdomen regardless of gestational age. ICRP guidance advises against PET-CT at every stage of pregnancy, not just in the first three months. MRI is appropriate and effective throughout and does not carry this limitation.

For most decisions made during pregnancy, yes. MRI shows the primary tumour, its local extent, and pelvic lymph node size well. It does not show metabolic tissue activity the way PET-CT does, and may not identify very small nodal deposits as reliably. Your oncologist will tell you specifically whether any gap in that information changes the treatment decision being made right now.

This is managed by a multidisciplinary team: your oncologist, a maternal-fetal medicine specialist, and a radiologist familiar with pregnancy imaging. MRI of the pelvis and abdomen is the main imaging tool. Treatment decisions — including those that involve the pregnancy — are made jointly by the team and discussed with you. Your oncologist will coordinate the right specialist support for your situation.

Yes, for a period after the scan. The radiotracer passes into breast milk, and a baby who feeds during this time would receive additional radiation. Your team will tell you exactly how long to pause — it depends on the specific tracer and dose used. Express and discard breast milk during the pause to maintain your supply. Do not resume before your team confirms it is safe to do so.

In rare exceptional circumstances, if PET-CT would urgently change a treatment decision and no alternative imaging can provide that information, the fetal risk may be weighed against the risk of delaying treatment. This decision involves the oncologist, obstetrician, a medical physicist calculating the estimated fetal dose, and the patient. It is reviewed at a multidisciplinary meeting before any decision is made — not by a single clinician acting alone.