U.K. sets pregnancy imaging guidelines

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Pregnant women should not undergo some types of medical exams that involve high doses of radiation to the fetus due to the small increased risk of causing childhood cancer, according to guidance developed by the Health Protection Agency (HPA), The Royal College of Radiologists and the College of Radiographers in the United Kingdom.

The guidance comes on the heels of a U.S. study that revealed radiologic exams on pregnant women have more than doubled over a 10-year timeframe.

The guidance published April 1 recommends that pregnant women should not be given ionizing radiation exams in which the fetus receives a dose of more than a few milligrays (mGy) - for example CT scans of the lower abdomen.

"It is recognized, however, that such examinations may sometimes be clinically justified by an overriding benefit to the health of the mother. If such examinations have taken place, the risk of causing childhood cancer would still be relatively small and termination of pregnancy would not be considered necessary," the authors wrote.

The guidance stresses that most medical exams that use ionizing radiation such as radiography, CT scans and nuclear medicine studies, involve fetal doses of less than, and often very much less than, 1 mGy. For these exams, the associated risks of childhood cancer are very low (less than 1 in 10,000) and much lower than the natural rate of childhood cancer (1 in 500). The guidance also indicates that the fetal radiation doses from all current medical examinations are too small to cause fetal death, malformation, retarded growth or impair the mental development of the unborn child.

"Even though the risk to the unborn child is much lower in the first few weeks of pregnancy - when a woman may not realize she is pregnant - the guidance recommends that certain very high dose examinations where the fetal embryo could receive a dose of more than 10 mGy should not be carried out on early unrecognized pregnancies. One way of preventing this is to restrict such examinations to the first 10 days of the menstrual cycle, when the woman is unlikely to have conceived," according to the guidance.

Roger Cox, director of the HPA's Center for Radiation, Chemical and Environmental Hazards said that while most medical exams using ionizing radiation are considered "extremely safe, a small number of procedures could result in the fetus receiving relatively high doses of radiation. The HPA's advice gives clear clinical guidance on how best to protect pregnant women and their unborn child during these medical examinations."