| Purpose of study. To assess whether there is an association between occupational exposure to low levels of ionizing radiation and risk of pregnancy ending in spontaneous abortion, and to estimate the magnitude of such an association. Methods. A retrospective cohort design was used to address the study question in an occupationally defined group. Members of the Canadian Association of Medical Radiation Technologists were mailed a questionnaire to ascertain pregnancy history. Respondents' occupational radiation dose records were obtained from the National Dose Registry by record linkage, and used to estimate pre-pregnancy radiation exposures for each individual pregnancy. A second mailed questionnaire was used to obtain more detailed information about exposures prior to and during a subset of the reported pregnancies. Risk of spontaneous abortion was determined for different levels of pre-pregnancy radiation exposure, and comparisons were made with an internal unexposed referent group. Results. Pregnancies with documented pre-pregnancy radiation exposure were observed to be at a small but significantly increased risk of ending in spontaneous abortion, as compared to those with no documented exposure (OR = 1.21; 95% CI 1.05--1.40). Risk was greatest in pregnancies with the highest cumulative pre-pregnancy dose. Less evidence of an association was observed among the more recent pregnancies and exposures. Conclusions . The results of this study indicate that occupational pre-pregnancy radiation exposures may increase the risk of spontaneous abortion, findings that are reasonably consistent with the few published reports of previous investigations of this relationship. However, in light of methodological limitations, the exact nature of the relationship between radiation exposure and risk of spontaneous abortion, and the precise levels of exposure associated with increased risk remain uncertain. Therefore, attempts to apply the findings of this study to modify regulatory limits would be premature, although efforts to include this outcome in the setting of such limits are warranted. Overall, these results reinforce the appropriateness of applying radiation protection principles that ensure that exposures to ionizing radiation are kept as low as possible for all workers at all times, regardless of existing evidence about specific health effects. |
