FRIDAY, Feb. 11 (HealthDay News) -- There's a small increased risk of cancer for children who had X-rays before they were 3 months old and those whose mothers had X-rays while pregnant, researchers say.

The new study findings highlight the need for doctors to be careful about using X-rays on pregnant women and infants.

In the study, Preetha Rajaraman, of the U.S. National Cancer Institute, and colleagues looked at the use of X-rays and ultrasound among 2,690 children with cancer and 4,858 healthy children who took part in the U.K. Childhood Cancer Study.

The mothers of 305 children underwent one or more X-ray examinations while pregnant (total number 319) and 170 children received at least one diagnostic X-ray examination in early infancy (total number 247). There were 13,723 ultrasound scans conducted during pregnancy and 138 conducted on young infants, the investigators found.

Children whose mothers had X-rays while pregnant had a slightly increased risk for all childhood cancers and for leukemia, though the increase was not statistically significant. Children who had X-rays in early infancy had a small, non-significant increased risk for all childhood cancers, leukemia and lymphoma.

Ultrasound was not associated with increased risk of cancer, according to the report published online Feb. 10 in BMJ.

"Our results, which indicate possible risks of cancer from radiation at doses lower than those associated with computed tomography scans, suggest a need for cautious use of diagnostic radiation imaging procedures to the abdomen/pelvis of the mother during pregnancy and in children at very young ages," the researchers concluded in a journal news release.

More information

The American College of Radiology, Radiological Society of North America has more about X-rays.