AJR: CT use growing in pregnant women
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Despite the undisputed value of CT in pregnant women in many emergency settings, spiking CT use in the general population and in smaller samples of pregnant women have heightened concern over radiation exposure to both patients and fetuses. "For pregnant women undergoing abdominopelvic CT, this concern is particularly relevant because the fetus, with a greater sensitivity to radiation than the mother, is also exposed to radiation and often is directly in the beam," according Shlomit Goldberg-Stein, MD, and colleagues from the department of radiology at Massachusetts General Hospital (MGH) in Boston.
Goldberg-Stein and co-authors reviewed all chest and abdominopelvic CT scans performed at MGH between 1998 and 2005, seeking to analyze utilization trends and indications among pregnant women as well as to estimate radiation doses and compare to trends in the population as a whole.
The authors found 74 chest and 86 abdominopelvic CT scans performed on 73 and 85 pregnant women, respectively. Over this eight-year study period, the incidence of chest CT grew by an average of 75 percent per-year per-1,000 deliveries, compared with 19 percent annual growth for the same examination among the general population. Abdominopelvic CT during pregnancy increased by an average of 22 percent per-year per-1,000 deliveries, compared with a 13 percent increase in the overall population. Neither of these rates among pregnant women differed significantly from overall population trends.
The average fetal dose administered was 24.8 mGy, with a range of 6.7 to 56 mGy. The 56 mGy exam was the only study to administer more than 50 mGy of radiation. Doses below this threshold are considered negligible, while a fetal dose of 100 mGy is estimated to increase the risk of childhood cancer by 0.1 percent, according to evidence cited by the authors.
Still, Goldberg-Stein and colleagues acknowledged that "[a]lthough there are no proven risks for the development of fetal malformation or mental retardation from ionizing radiation at levels of diagnostic imaging, a much debated, theoretic increased risk of carcinogenesis remains for all levels of radiation exposure."
The most common indications for chest CT were suspected pulmonary embolism (accounting for 63 of 74 exams) and suspected pulmonary nodule (7 of 74 exams). Among abdominopelvic studies, right lower quadrant pain with suspected appendicitis accounted for 50 of 86 studies, while trauma and nonspecific abdominal pain made up 14 and 11 of the additional studies, respectively.
Goldberg-Stein and co-authors concluded that the number of abdominopelvic CT scans in pregnant women, a higher-dose procedure because the beam is targeted more directly at the fetus, could be significantly reduced. "[W]ith suspected appendicitis, ultrasound and MRI—neither of which delivers ionizing radiation— are alternatives to CT for imaging evaluation. ... [W]hen CT is reserved as a third-line tool after ultrasound and MRI prove inconclusive, the literature suggests that only a small proportion of pregnant women with suspected appendicitis would require CT."
The authors pointed out that their findings might bear limited generalizability due to their study's single-institution design, although they found that their observed utilization rates differed little from previous studies. Additionally, the authors were forced to estimate dosimetry for manually set exams, which could have resulted in miscalculations by up to 50 percent in a minority of patients.
The researchers indicated that, with specifically outlined guidelines, "abdominopelvic CT can be safely performed with negligible fetal risk."
"Whether CT is overused in the general population is a subject of much debate," the authors continued. "Nevertheless, the large increases in CT examination rates in the pregnant patient during the past decade do not clearly indicate overutilization specific to this patient population. Of course, growth of CT proportionately both in the pregnant population and in the overall population may still represent overuse throughout."