Radiology and the Pregnant Patient Q&A
Is there a safe level of radiation exposure from medical x-ray exams for a pregnant patient?
There are no dose limits for radiation exposure of patients. There are, however, imaging exams that can be performed safely during pregnancy, especially those that do not involve exposure of the lower pelvis. The decision to use radiation must be justified by the physician ordering the exam, depending upon the individual patient situation. When it has been decided that a medical procedure is justified, the procedure should be performed such that a good diagnostic exam is obtained with the lowest possible patient radiation dose.
What is the 10-day rule?
The 10-day rule was established by the International Commission on Radiological Protection to minimize the potential for performing x-ray exams on pregnant women. The basis of the rule was to do abdominal and pelvic x-ray exams only during the 10 days following the onset of menstruation. We know much more today about radiation and pregnancy, and we know that substantial doses (~10 rem; more than is received from routine diagnostic medical x-ray exams) are necessary to cause birth defects or malformations. Since organogenesis starts 3 to 5 weeks postconception, it was felt that radiation exposure in early pregnancy couldn't result in malformation. Now the focus is shifted to a missed period and the possibility of pregnancy. If there is a missed period, a female should be considered pregnant unless proved otherwise. In such a situation, every care should be taken to explore other methods of getting the clinical information by performing exams that do not use ionizing radiation.
What if a patient underwent an abdominal or pelvic x-ray exam before realizing that she was pregnant?
The radiation dose to the unborn child should be estimated by a medical physicist/radiation safety specialist experienced in dosimetry. The patient can then be advised about potential risks. In nearly all cases, there is little risk or no risk. In a few cases, perhaps with multiple abdominal or pelvic CT exams (1.2-3 rad to the unborn child per exam), the dose involved may be higher. It is extremely rare for the dose to be high enough to warrant advising the patient to consider terminating the pregnancy (approximately 15 rad).
How safe are x-ray exams of the chest and extremities, etc., during pregnancy?
Diagnostic x-ray exams of areas that do not include the lower pelvis can be done safely during pregnancy.
Can cardiac catheterization be performed on a pregnant patient?
Yes, after the benefits and risks of waiting to perform the exam after delivery have been considered. The potential radiation exposure of the unborn child from a cardiac catheterization (or higher-exposure exams of the upper abdomen and lungs) is from radiation that scatters from the main area of interest to the lower pelvis. This amount of radiation exposure is very small, but it is still important to optimize the parameters to keep the exposure as low as possible. Ways to keep the exposure low (or zero) include keeping the x-ray beam size as small as necessary for the clinical purpose, taking care about the direction of the primary beam so that it is not going close to the lower pelvis, selecting technique factors that will give a good diagnostic result with a low radiation dose, and keeping the beam on time to a minimum. If these considerations are taken into account, the radiation exposure to the unborn child would be very small and certainly below levels known to cause effects.
It should be noted that in some practices, a lead apron is used (either on the patient or under the patient on the table) with the idea that the exposure will be less. These ideas have little merit and, because the apron may rescatter photons back into the body, are not recommended. However, there is reason to use an apron if the apron is being used to block an unwanted portion of the primary beam from getting to the lower pelvis.
Are there recommendations regarding termination of pregnancy after radiation exposure?
Recommendations for termination of pregnancy at fetal doses of less than 100-150 mGy are not justified based upon radiation risk, according to ICRP 84 and Wagner and colleagues. At fetal doses above this level, the decision should be based upon the individual circumstances. This complicated issue involves much more than radiation protection considerations and requires the provision of counseling for the patient and her partner.
At fetal doses in excess of 500 mGy, there can be significant fetal damage, the magnitude and type of which is a function of dose and stage of pregnancy. As can be seen in Table 1, diagnostic x-ray exam radiation doses do not approach these levels.
Table 1. Fetal dose estimates for common diagnostic x-ray procedures.
(Adapted from Sharp, Shrimpton, and Bury, 1998).
Can a patient become sterile after undergoing a diagnostic x-ray examination?
No. The threshold radiation dose for temporary sterility is approximately 150 mGy for men and 650 mGy for women. The threshold radiation dose for permanent sterility is 3,500 mGy for men and 2,500 mGy for women. The dose to the gonads from diagnostic x-ray exams is well below these thresholds.
Can a pregnant employee continue to work in an x-ray department?
Yes, a pregnant worker can continue working in an x-ray department. An assessment of her dosimetry history should be undertaken to assure that the fetal dose can be kept below 5 mGy (the limit in the United States). If radiation exposures are such that 5 mGy during gestation could be exceeded, efforts must be made to reduce the dose. If radiation exposures are not expected to approach 5 mGy, it is not necessary to reassign the worker. The worker must be informed of the potential risks, local policies, and recommended dose limits.
Some options that can be considered for the pregnant worker are (1) no change in assigned working duties assuming the dosimetry evaluation shows there is little chance in exceeding the 5 mGy limit, (2) change to another area where the radiation exposure is lower, or (3) change to a job that has essentially no radiation exposure.
It should be noted that the dose limit applies to the fetal dose. This is not the dose measured on a personal dosimeter. A personal dosimeter worn at the waist by diagnostic radiology workers is likely to overestimate fetal dose. If the dosimeter is worn outside a lead apron, the measured dose is a significant overestimate and, while it can be used as an upward bound on fetal dose if no other information is available, is not recommended for use in estimating fetal dose. Fetal doses are not likely to exceed 25 percent of the personal dosimeter measurement.
How high is the chance that a pregnant staff member will approach the dose limits of exposure?
If proper radiation protection measures are used, it is not at all likely that a pregnant worker in a radiology department will approach the limits on fetal dose. While radiation doses to the worker in a fluoroscopy suite will be higher, the leaded apron will keep exposure at the waist level very small, if even measurable.
How do I counsel patients on radiation dose and risk?
Pregnant patients who are concerned about the exams prior to their being performed should be counseled, first, on whether the unborn child is expected to receive any radiation dose as a result of the exam (e.g., no dose for a chest or extremity x ray) and, second, on any risk the exam has for the pregnancy. For diagnostic radiological exams, it is unlikely the radiation dose to an unborn child will be high enough to result in harmful effects. Pregnant patients who are concerned about the radiation exposure after the exam has been performed should be counseled on whether the unborn child received any radiation dose as a result of the exam (e.g., no dose for a chest or extremity x ray). If it has been determined that the unborn child did receive some radiation dose, tables of fetal dose (such as Table 1) can be used as an estimate of the dose received and can be used during counsel. If the patient wants specific information on fetal dose, a dosimetry assessment can be performed by a trained medical or health physicist. This assessment can take 1-2 weeks and the results given to the physician to discuss with the patient.
What are the effects of exposure in utero?
Unless a high number of diagnostic radiological exams of the pelvic area are performed during pregnancy, radiation from routine exams will not result in harmful effects. Prenatal doses from properly performed diagnostic procedures present no measurable increase in the risk of prenatal death, malformation, or impairment of mental development over the background incidence of these effects.
The effects of exposure to high amounts of radiation (>100 mGy) depend on fetal age and total absorbed dose. Radiation risks are most significant during organogenesis and the early fetal period, somewhat less in the second trimester, and least in the third trimester. CNS sensitivity is highest about the eighth week postconception; fetal doses in the range of 1,000 mGy result in a high probability of severe mental retardation.
Throughout most of pregnancy, the unborn child is assumed to be at about the same risk for potential carcinogenic effects of radiation as are children. According to Wagner and colleagues, the percent likelihood of NOT developing cancer is 99.93 percent with no radiation exposure (i.e., all pregnancies have a 0.07 percent chance that the child will develop cancer during childhood). With an in utero radiation exposure of 10 mGy, the chance of not developing cancer is between 99.75 and 99.88 percent. With an in utero exposure of 50 mGy, the chance of not developing cancer is between 99.12 and 99.70 percent.
This Q&A Web page was adapted from the IAEA's Pregnancy and Radiation Protection in Diagnostic Radiology Web page.
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