Research shows CT and nuclear imaging tests during pregnancy do not boost the risk of childhood cancer

Pregnant women who undergo CT or nuclear imaging tests during pregnancy do not appear to have babies at higher risk of developing childhood cancer, says a new study led by St. Michael’s Hospital physician and Institute for Clinical and Evaluative Sciences (ICES) researcher Dr. Joel Ray.

The study of 1.8 million mother-child pairs in Ontario identified 5,590 women who had a major radiodiagnostic test (CT or nuclear imaging) during pregnancy, now performed in about 1 in 160 pregnancies.

Researchers found while the probability of babies developing childhood cancer was less than one in 1000, the rate of diagnosed childhood cancer was actually lower in the children exposed to a major radiodiagnostic test.

“Cancer is a leading cause of hospitalization and death among children 14 and younger yet, we observed no higher risk to the child after CT or nuclear imaging during pregnancy,” Dr. Ray said, “Our findings signal that, when necessary, major radiodiagnostic testing during pregnancy should be carried out, along with brief counseling of the mother.”

“These imaging tests may be especially important during pregnancy, when major illnesses like lung clots or appendicitis can be missed,” he added. “Delaying the diagnosis of such conditions may postpone therapy, in turn, jeopardizing both mother and child,” Dr. Ray said.

According to the researchers, the overall rate of exposure to major radiodiagnostic testing in pregnancy rose from 3.0 per 1,000 in 1991 to 6.3 per 1,000 livebirth pregnancies in 2008. About 73 per cent of all major radiodiagnostic tests were CT scans. Of those, 68 per cent were of an extremity or the head, nearly 10 per cent of the chest and nearly 23 per cent of the abdomen, spine or pelvis.

While scientific research on the relation between radiation exposure and childhood cancers is conflicting, the researchers strongly recommend that a urine pregnancy test continue to be done in all potentially pregnant women before undergoing radiodiagnostic testing, and that lead apron shielding be used in all women of reproductive age.

The study "Major radiodiagnostic imaging in pregnancy and the risk of childhood malignancy: a population-based cohort study in Ontario" is in the September 7, 2010 issue Open-Access journal PLoS Medicine.

• About St. Michael’s
• St. Michael’s Hospital provides compassionate care to all who walk through its doors. The Hospital also provides outstanding medical education to future healthcare professionals in more than 23 academic disciplines. Critical care and trauma, heart disease, neurosurgery, diabetes, cancer care, and care of the homeless are among the Hospital’s recognized areas of expertise. Through the Keenan Research Centre and the Li Ka Shing Knowledge Institute, research at St. Michael’s Hospital is recognized and put into practice around the world. Founded in 1892, the Hospital is fully affiliated with the University of Toronto.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.

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