Possible biological effects of radiation exposure of the developing fetus in utero include prenatal death, intrauterine growth suppression, microcephaly, retarded mental development, organ malformations, and childhood tumors. The hazard of each effect depends on the gestational age at the time of exposure, the cellular repair function of the fetus, and the absorbed dose. By comparison of the dose levels that cause these risks with the dose to the fetus at the time of routine radiography, the risk to the fetus is small, so although pregnant women are protected by the International Radiation Protection Association, the National Council on Radiation Protection, the American Radiological Society, and the American College of Obstetricians and Gynecologists, medical examinations by radiation or nuclear should not be interfered with by the refusal of a pregnant woman if they can provide important diagnostic information. Although the risk is minimal, make sure that the radiation dose is minimized to the extent that it is effective. INTRODUCTION Radiologic examinations of pregnant women are difficult to perform because of the radiation hazards they can be exposed to. This article reviews and analyzes the effects of exposures on pregnant women, distinguishes between specific maternal doses and routine exposure doses, outlines the views of international, national, and professional organizations that consider diagnostic radiological examinations to be hazardous, and describes the indications for appropriate diagnostic examinations of pregnant women. This paper studies pregnant women, but the data sources were collected when the pregnant women themselves were unaware of the pregnancy or did not declare it. Effects of Radiation Exposure on Pregnant Women The data that suggest that pregnant women exposed to radiation will have possible biological effects are from animal experiments and exposed humans. The original source of human data was the survivors of the atomic bombings of Hiroshima and Nagasaki in 1945, including about 2,800 exposed pregnant women, 500 of whom received doses in excess of 10 mGy. The effects that can occur in pregnant women after exposure to radiation include prenatal deaths, intrauterine developmental disorders, microcephaly, severe neurological delays, low intelligence quotient (IQ), organ malformations, and childhood tumors. It is the exposure dose and the stage of pregnancy at the time of exposure that determine these effects (Table 1-2). Factors in Applying a Specific Dose-Exposure and Fluoroscopy If the uterus is located outside the exposure field and the radiation strikes only the pregnant woman, the dose to the pregnant woman is small, and the dose to the pregnant woman is high when the uterus is located inside the exposure field. In these examples, the dose of radiation acting on the pregnant woman from exposure or fluoroscopy depends on the thickness of the patient, the direction of projection, the distance of the pregnant body from the body surface, and x-ray technical factors. The dose acting on a pregnant woman can change by a factor of about 10 depending on any one of these factors for a particular examination or projection. Our association’s estimates of maternal doses for exposure and fluoroscopy examinations in early pregnancy are shown in Table 3, and these values can be compared to the naturally occurring maternal dose of background radiation of 0.5C1mSv to which pregnant women are exposed throughout the course of pregnancy. If the site of projection is outside the pregnant body, a lead sheet can be used to shield the site outside the projection and also the pregnant body. Although scattered rays are rare, beginners should also be reminded to use a lead sheet to cover the area, even though it may not make sense for protection, it can give the patient peace of mind with the feeling of being protected. CT Compared to plain radiographs, CT radiation exposure dose levels are higher, and the gestational body dose varies with the distance from the uterus to the scanning level, the patient’s body thickness, the depth of the gestational body, and x-ray technical factors; a change in one factor for a particular exam can change the gestational body dose by a factor of two to four. Our Society’s estimates of gestational body dose for abdominal and other site examinations are shown in Table 4, and these estimates vary somewhat as the image quality and/or scanning range of the examination can be reduced when image technology permits. Some CT manufacturers introduce automatic exposure control features that provide real-time tube-ball current correction based on tissue attenuation. Such devices can reduce the amount of wire exposure in small-bodied patients and, in the case of pregnant women, prevent unnecessarily high tube-ball volume settings. For large-bodied patients, the exposure dose needs to be increased for image quality, which also allows more of the dose to be absorbed by adipose tissue, and therefore is not linear with the tube-bulb current setting for internal organs. Monte Carlo simulations show that a twofold change in a scanning parameter results in only a 25% change in effective dose for large patients (100 Kg, body width less than 50 cm), because the effective dose depends mainly on the organs reached. In the case of pregnant women, accurate positioning is more important to reduce the radiation hazard than minimizing the radiation dose. Before CT scanning, tube current and tube voltage can be pre-set, and exposure is best accomplished with automatic exposure control. Although the flash rays are small during CT examination, if the abdomen and pelvis are not in the scanning field, they can also be shielded with lead, which can reassure the patient and reduce the risk to beginners. Nuclear Medicine The dose of radionuclide examination in pregnant women depends mainly on the uptake and metabolism of the maternal radiopharmaceutical, the dose through the placenta and the uptake by the pregnant body. Estimates of the absorbed dose to the pregnant body for our association are shown in Table 5. Policy Description Several recognized published documents provide guidance for radiologic examinations of pregnant women.In 1977 the National Council on Radiation Protection and Measurements issued the following statement: exposure doses below equal to or less than 50 mGy pose little harm and are negligible compared with other risks of pregnancy. Only at doses greater than 150 mGy does the risk of malformations increase significantly with increasing dose, and it is rare for a pregnancy to become terminated on its own as a result of fetal radiation exposure from diagnostic tests. The American Radiological Society has established the following principle for the use of abortion: termination of pregnancy due to harm to the embryo or fetus from radiologic examination is a very extreme practice. The International Society for Radiological Protection (ISRP) has issued a statement that the presence of most appropriate radiologic procedures does not significantly increase the number of prenatal deaths, malformations, or mental retardation in comparison to control groups. In addition, it states that fetal doses below 100 mGy are not grounds for termination of pregnancy. More recently, the American College of Obstetricians and Gynecologists issued the following statement: Pregnant women should be cautioned that the diagnostic procedure of a single x-ray exposure will not cause fetal harm, especially if less than 50 mGy, and will not cause fetal malformations and miscarriages. With these statements and the data in Tables 1 and 2, it is clear that fetal doses less than 50 mGy produce negligible radiological harm, and Table 2 shows that at doses greater than 50 mGy at 100 mGy the increase in organ malformations and childhood tumors is only 1% compared to the control group. DEVELOPED PRACTICE POLICIES AND GUIDELINES The development of an association’s practice policies on radiographic imaging of pregnant women should be a process of data accumulation that is achieved through a review of the available literature and the various guidelines issued by the various professional radiological protection organizations as much as it is a review of the risks of accepted best practices. In our practice, we follow the guidelines for providing imaging to pregnant women with the presence of conventional medical symptoms. One of the indications considered in our analysis was imaging to assess urolithiasis in pregnant women, in which case ultrasound is the imaging modality of choice, ultrasound that includes not only the kidneys, but also the bladder to assess ureteral jet activity, and negative ultrasound to check for ureteral terminal stones. Negative ultrasound is safe at any stage of pregnancy unless membranes rupture, which is an important relative contraindication. If the initial examination does not reveal an abnormality, a second examination should not be performed until 24 hours later. If both examinations are inconclusive and the clinical diagnosis is urolithiasis with persistent pain or fever, other imaging methods should always be considered before treatment. The value of CT plain scanning for the detection of urolithiasis is well established.CT is more effective than excretory urography in detecting urinary stones, with sensitivity and specificity ranging from 92% to 99%.CT is also superior to urography for the diagnosis of complex stone disease.CT can characterize abnormalities of the urinary tract contours and has advantages for nonstone abdominal pain, making it the primary imaging method for patients with suspected urolithiasis.CT is also a useful imaging modality in the diagnosis of urolithiasis, as it can describe abnormalities of the urinary tract contours and has advantages for nonstone abdominal pain. Moreover, CT is fast, noninvasive, and easy to perform, and unlike secretory imaging, CT can be performed without the use of contrast media. Considering the radiation dose of CT to the pregnant body, clinical consideration has also been given to replacing CT with intravenous pyelography (Fig. 2).Intravenous pyelography images include unenhanced images, renal contrast images, secretory phase, renal images, ureter and bladder, and the injection takes about 15-20 minutes to complete, and the delayed images are helpful in determining the level and degree of urinary tract obstruction. We assessed the pregnant body dose by a certain number of both CT and IVP imaging methods. These analyses must examine patients with different body thicknesses (Fig. 3) because the radiation dose examined increases significantly with maternal girth, which is typically later when urolithiasis is most common. the CT scanning parameters are altered to a lesser extent than the patient dimensions, e.g., as shown in Fig. 3 the patient’s body thickness becomes the same as the range, and the CT radiographic output is 3 rather than the phasic radiographic curve.10 For smaller patients, the radiographic output should be reduced, and peripheral attenuation will be reduced, resulting in an increase in the internal radiation dose associated with the surface dose. For large-sized patients, the ray output increases and the surrounding attenuation increases, resulting in a decrease in the internal irradiation dose associated with the ray output. When the scan output is adjusted with patient size, the organ dose is a relative constant, and automatic exposure control is particularly well suited for scan outputs that are adjusted based on patient attenuation. By our calculations, the fetal radiation dose from CT is lower than IVP for patients with body thicknesses greater than 25 cm (Fig. 3). In our extensive radiology practice, the average body thickness of patients is 24 cm, and most pregnant women in the middle and last trimesters have a body thickness of at least 25 cm. Based on these data, and taking into account the residual dose of CT scanning in the abdominopelvic region, we can arrive at a consistent rule for the evaluation of pregnant women suspected of having urinary stones, and for patients with suspected urolithiasis, who have had two consecutive inconclusive comprehensive ultrasounds, a CT scan should be performed. CT should be performed. The same process of accumulating data can lead to other imaging guidelines, such as that done by Winer-Muram on pulmonary embolism in pregnant women, where WinerMuram and colleagues calculated the maternal dose from CT examination of pregnant women with pulmonary embolism and found it to be less than that from nuclear medicine pulmonary ventilation at any stage of the pregnancy, which is consistent with our data and other published data. These data are necessary, especially for a pregnant woman with suspected pulmonary embolism who requires us to provide an appropriate means of examination.CT pulmonary angiography has a sensitivity of up to 86%, a specificity of up to 94%, and greater discriminatory power for normal or near-normal pulmonary ventilation thresholds than does pulmonary ventilation. The combination of spiral CT and ultrasound for pulmonary embolism in outpatients can result in a diagnostic yield of 99%, and spiral CT is equally useful for pulmonary embolism in nonpregnant patients. The process of evaluating pulmonary embolism has also been documented in the literature on pregnant women, and 31% of respondents recommended this argument. Therefore when lower extremity ultrasound fails to diagnose pulmonary embolism, CT is the second most appropriate method to confirm the diagnosis. Overall Clinical Guidelines As shown in Table 3-5, the maternal dose from routine radiography, fluoroscopy, CT, and nuclear medicine examinations is significantly lower than the identified risk threshold of 50-100 mGy. Of note is that head, neck, chest, and extremity imaging have negligible risk to the pregnancy, and for abdominal and pelvic imaging, ultrasound is used as a preferred option because of the absence of ionizing radiation to the pregnancy.MR imaging is the most appropriate method of diagnosis in cases where abdominal or pelvic ultrasound is not diagnostic available as a further test, but MR is more restrictive. Since the maternal dose from a single abdominopelvic CT is small enough not to affect fetal health, abdominopelvic CT can be performed to provide useful information and maternal condition after the failure of the non-radiographic methods. Conclusions Radiation doses released by radiographic, fluoroscopic and CT examinations of the nonabdominopelvic region are small for the fetus, and doses from radiographic, fluoroscopic, CT and nuclear medicine studies of the abdominopelvic region rarely exceed 25 mGy. After comparing data from general radiographic and nuclear medicine examinations with hazards, we conclude that the absolute risk to the fetus (including induction of childhood tumors) is small at a gestational body dose of 100 mGy, and when the dose is below 50 mGy is negligible. This information ensures that pregnant women and their husbands minimize the risk of radiation exposure to the uterus by using conservative clinical measures when faced with the risk of mandatory or unexpected radiation exposure. Radiography or nuclear medicine examinations should be performed only when necessary, and, as with medications or treatments for pregnant women, the dose should be minimized as much as reasonably possible.