Avoid exposure of the abdomen to ionizing radiation during pregnancy, especially during the first trimester. Diagnostic procedures involving the use of radiopaque contrast agents should be carried out under the direction of qualified, trained personnel and in facilities equipped to handle emergencies which may arise from severe reactions to the contrast agent. After intravascular administration of a radiopaque agent, competent personnel and emergency facilities should be available for at least 30 to 60 minutes, since severe delayed reactions have been known to occur. These severe, life threatening reactions suggest hypersensitivity to the radiopaque agent. This has prompted the use of several pretesting methods, none of which can be relied upon to predict severe reactions.
Many authorities question the value of any pretest.
A history of bronchial asthma or allergy, a family history of allergy, or a previous reaction to a contrast agent warrant special attention. Such a history, by suggesting histamine sensitivity and a consequent proneness to reactions may be more accurate than pretesting in predicting the likelihood of a reaction, although not necessarily the severity or type of reaction in the individual case. The sensitivity test most often performed is the slow injection of 0.5 to 1.0 mL of the radiopaque medium, administered i.v., prior to injection of the full diagnostic dose. Successive small increments are used over several minutes if the patient has a history of allergy. An impending reaction is often indicated by respiratory difficulty, faintness, sneezing, itching, vomiting, or urticaria.