## 4 Discussion  
The simulation of the most frequent clinical scenarios involving pregnant patients and ionizing radiation diagnostic and interventional procedures (Table 2) showed a large range of possible fetal doses (Table 4) in these procedures. Nevertheless, in scenarios when the fetus is not in the primary beam, such as CTPA, CT for ischemic stroke, nephrostomy placement, or two-pass mechanical thrombectomy, the fetal head and body doses were well below 1 mGy (Table 4). This is in line with already reported values [18; 19; 20; 21; 22; 23; 30; 31; 32]. Such radiation doses further reinforce the fact that these procedures should not be postponed if the only contraindication is fear of fetal radiation. Since fetal dose estimation is usually not necessary unless the dose to the fetus is expected to be above 1 mGy [14; 15; 20], further investigation of fetal doses was focused on clinical scenarios with a fetus within the beam. These scenarios included abdominal radiography and CT for polytrauma in three large teaching hospitals using four radiography units and eight CT units (Table 3). Measured fetal doses ranged from 0.9 mGy to 1.9 mGy in abdominal radiography (Figure 2). This is in line with previous findings where fetal doses of up to 3 mGy were reported [17]. Although fetal doses in abdominal radiography were rather consistent in all three hospitals, it is worth noting that different imaging protocols were used. Protocols consisted of one or two patient positions. This difference was found between hospitals, but also in Hospital 1 (Table 3). Although still in use, abdominal radiography is of limited diagnostic value in a patient presenting with abdominal pain. According to the guidelines, anteroposterior projection with a patient in the supine position is a preferred method, used in a clinical scenario of suspected bowel obstruction and urinary tract calculosis [33]. If there is a clinical suspicion of possible bowel perforation, additional anteroposterior projection  
Figure 2: Absorbed dose for each specific scenario measured in the fetal head and body in three hospitals. NAP—non-specific abdominal pain; NA— nephrolithiasis, appendicitisitis, abdominal pain; P—polytrauma; R—radiography unit as labeled in Table 3; CT—computed tomography unit as labeled in Table 3; H—hospital. The line represents a fetal dose of 50 mGy, which the American College of Radiology suggests as an upper threshold for pelvic CT imaging protocols for a pregnant patient [29]. Uncertainty of the mean is presented with SEM. with a patient in an erect position adds valuable clinical information; therefore, in several instances in this study, both patient positions were used. This underlines importance of a clear clinical question in referral. Nevertheless, the largest fetal dose was found in Hospital 2, which used imaging in only one patient position. This shows that attention toward the optimization of imaging procedures is required. When a clinical question for abdominal pain was set, NCCT was a preferred scanning protocol since it also allows for the detection of urinary tract calculi, which might not always be detected on post-contrast scans. After the evaluation of NCCT scans, the radiologist might add an additional scan in the post-contrast arterial or portovenous phase. Although the standardization of all protocols is of utmost importance, it is particularly challenging in a pregnant patient, where the presentation of various clinical scenarios can differ from a non-pregnant patient. Therefore, individualized scanning protocols based on relevant clinical information are often used. In Hospital 2, a specific low-dose protocol for kidney stones was used with the low fetal dose of 2.2 mGy in one CT unit. All abdomen protocols used were routine abdomen protocols with fetal doses ranging from 8.6 mGy to 23.7 mGy (Figure 2). This reveals a fetal dose max/min ratio of approximately three if the procedure is performed in a different hospital or even in the same hospital, but on a different unit.