Safety is a matter of taking appropriate actions to limit the risk to a level well justified by the benefit. To maintain a high standard of safety, particularly when imaging pregnant or potentially pregnant patients, the degree of medical benefit should outweigh the wellmanaged levels of risk. This practice parameter has been developed to provide current practical information to radiologists, including nuclear medicine physicians, other physicians, and medical practitioners implementing policies for imaging pregnant and potentially pregnant patients. Individual institutions and facilities should develop their own policies. As with all imaging procedures, the specifics of an individual case should always be considered and may lead to the modification of even the most strongly suggested guidelines. Throughout this practice parameter, the radiologic or nuclear medicine/positron emission tomography (NM/PET) technologist is referred to as the most likely person to communicate with the patient about the potential risks for pregnant patients. Nurses, registered radiologist assistants, physician assistants, physicians, and other staff, such as receptionists, might also fill this role. Therefore, whenever this practice parameter refers to technologists, it should be understood that others may share or be assigned this responsibility. When managing a pregnant patient who was potentially exposed to a high dose of radiation, the radiologist or nuclear medicine physician should involve a Qualified Medical Physicist to estimate absorbed dose to the conceptus from the diagnostic or interventional procedures, either prospectively or retrospectively. The Qualified Medical Physicist should also advise the radiologist regarding the means by which risk can be reasonably limited. Scope This practice parameter addresses the imaging of pregnant and possibly pregnant patients with ionizing radiation (ie, radiography, fluoroscopy, computed tomography [CT], and diagnostic NM/PET). It does not address issues related to imaging the lactating woman, the use of contrast agents during imaging, or magnetic resonance imaging (MRI; see the ACR Manual on Contrast Media and the ACR Guidance Document on MR Safe Practices [2,3]). Furthermore, this practice parameter addresses neither pregnant or potentially pregnant patients undergoing radiation or radionuclide therapy nor pregnant or potentially pregnant personnel working with ionizing radiation. Objective The objective of this practice parameter is to assist practitioners to identify pregnant patients, prevent their unnecessary radiation exposure, tailor examinations to effectively manage radiation dose, and develop strategies to quantify and evaluate the potential effects of radiation delivered to pregnant patients. This practice parameter : 1) outlines the body of knowledge on the risks to the conceptus from ionizing radiation during the various stages of pregnancy, 2) provides guidance on when and how to screen for pregnancy prior to imaging examinations PRACTICE PARAMETER 3 Pregnant or Potentially Pregnant Patients using ionizing radiation, 3) recommends means to control, manage, and practically minimize radiation dose to pregnant or potentially pregnant patients, and 4) discusses evaluation of dose assessment, risk assessment, and communication issues following exposure of pregnant patients. II. RADIATION RISKS TO THE CONCEPTUS Potential effects of radiation have been extensively researched, resulting in a broad body of knowledge. As with any body of knowledge, uncertainties exist. The purpose of reviewing radiation research and the underlying uncertainties is to build a knowledge base from which reasonably informed clinical decisions can be reached about the risks of radiological examinations in pregnant or potentially pregnant women. The risk assessment should address the likelihood of an adverse outcome and the severity of the outcome. These should be weighed against the potential benefits to the pregnant patient and to the conceptus. The following information (Table 1) can be used to gain perspective and develop clinical guidelines in the management of pregnant or potentially pregnant patients. A more complete review is provided in Appendix A. Table 1: Summary of Suspected In Utero Induced Deterministic Radiation Effects*[4,5] Menstrual or Gestational age Conception age <50 mGy (><5 rad) 50–100 mGy (5–10 rad) >100 mGy (>10 rad) 0–2 weeks (0–14 days) Prior to conception None None None 3rd and 4th weeks (15–28 days) 1st–2nd weeks (1–14 days) None Probably none Possible spontaneous abortion. 5th–10th weeks (29–70 days) 3rd–8th weeks (15–56 days) None Potential effects are scientifically uncertain and probably too subtle to be clinically detectable. Possible malformations increasing in likelihood as dose increases. 11th–17th weeks (71–119 days) 9th–15th weeks (57–105 days) None Potential effects are scientifically uncertain and probably too subtle to be clinically detectable. Risk of diminished IQ or of mental retardation, increasing in frequency and severity with increasing dose. 18th–27th weeks (120–189 days) 16th–25th weeks (106–175 days) None None IQ deficits not detectable at diagnostic doses. >27 weeks (>189 days) >25 weeks (>175 days) None None None applicable to diagnostic medicine. *Stochastic risks are suspected, but data are not consistent [6]. For exposure to a newborn child, the lifetime attributable risk of developing cancer is estimated to be 0.4% per 10 mGy (1 rad) dose to the baby. The potential risks in utero for the second and third trimesters and part of the first trimester may be comparable, but the uncertainties in this estimate are considerable. III. SCREENING FOR PREGNANCY According to the International Commission on Radiological Protection (ICRP), thousands of pregnant women are exposed to medically indicated ionizing radiation each year [4]. The frequency at which pregnant patients are unintentionally exposed to ionizing radiation is unknown. One study reported that 1% of women of child-bearing age who underwent abdominal imaging were unknowingly pregnant in their first trimester [7].