• Home
  • Pregnancy &           
  • Bookshop
  • Contact us
  • Donate now
  • Frequently Asked Questions
  • Please read

Our Helplines

1-877-439-2744 Motherisk Helpline
1-800-436-8477 Morning Sickness
1-877-327-4636 Alcohol and Substance
1-866-937-7678 Exercise in Pregnancy
1-888-246-5840 HIV and HIV Treatment
416-813-6780 Motherisk Helpline

The Cancer in Pregnancy Forum

Archived Questions and Answers
This Forum has been the centre of an exceptional exchange of knowledge diagnosis, treatment, symptoms and other effects of cancer during pregnancy and lactation. All are welcome to review the Questions and Answers posted here, provided that they acknowledge and accept the important proviso and disclaimer below.
Submit a question
Forum > Cancer - Active Topics: Cancer - Active Topics
PET Scan During Pregnancy

Date: 2009-11-03

I am approx 5 weeks pregnant but 3.5 months ago, i had a whole body scan (with 5 milicuries of radioactive iodine) and a PET scan done as my doctor suspected that my thyroid cancer had returned. i had thyroid cancer over 20 years ago and it was removed with radioactive iodine treatment after the surgery. i am concerned about the risks to my pregnancy and baby. could you please let me know what type of risk the whole body scan and PET scan pose as they were fairly recent? all research i have read suggested 12 months after radioactive iodine treatment though i believe those were in reference to cancer treatment vs. just diagnostic testing. thanks!


If you are a patient, consult your physician. The following should not replace the assessment and advice you have been receiving or may receive from your physician (cancer specialist, obstetrician or other healthcare provider). It is offered for your information only.

The maximum amount of radiation that is considered permissible for fetal exposure is 50 Milligray units. The fetal radiation dose following a single PET-scan is unlikely to be higher than this level.

The location of the PET-scan as well as the frequency will influence the amount of fetal dose of radiation, and it is important for the technician to calculate the amount of maternal and fetal dose prior to the procedure.Since the PET scan was performed about 10 weeks prior to conception, there was no fetal exposure to the radiation.

With respect to the radioactive iodine used, the half life is about 8 days, which is the time it takes for half of the initial dose to be eliminated. Generally it is agreed that by 5 half lives, almost all of the drug is eliminated. Also fetal thyroid doesn't begin absorption and incorporation of the iodide till the tenth week of gestation, thus exposure during early gestation shouldn't pose a high risk. The small dose used for diagnostic purposes as well as the 10 week lapsed time prior to your conception, minimizes if not eliminate any type of exposure to the fetus, and we don't suspect an increased risk to the baby in this situation.

Valid XHTML 1.0 Transitional [Valid RSS]

* - "MOTHERISK - Treating the mother - Protecting the unborn" is an official mark of The Hospital for Sick Children. All rights reserved.

The information on this website is not intended as a substitute for the advice and care of your doctor or other health-care provider. Always consult your doctor if you have any questions about exposures during pregnancy and before you take any medications.

Copyright © 1999-2015 The Hospital for Sick Children (SickKids). All rights reserved.

The Hospital for Sick Children (SickKids) is a health-care, teaching and research centre dedicated exclusively to children; affiliated with the University of Toronto. For general inquires please call: 416-813-1500.

  |  Contact SickKids  |  Terms of Use