Pregnant women should not undergo some types of medical examination that involve high doses of radiation to the foetus because of the small increased risk of causing childhood cancer, according to guidance developed by the Health Protection Agency, The Royal College of Radiologists and the College of Radiographers.
The guidance recommends that pregnant women should not be given ionising radiation examinations in which the foetus receives a dose of more than a few milligrays (mGy) – for example, CT scans of the lower abdomen. It is recognised, 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 guidance stresses that most medical examinations that use ionising radiation – which include X-rays, dental X-rays, CT scans and nuclear medicine scans – involve foetal doses of less than, and often very much less than, 1 mGy. For these examinations the 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 foetal radiation doses from all current medical examinations are too small to cause foetal 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 realise she is pregnant – the guidance recommends that certain very high dose examinations where the foetal embryo could receive a dose of more than 10 mGy should not be carried out on early unrecognised 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.
