Pregnancy Outcome After I-131 Therapy for Patients With Thyroid Cancer: A Nationwide Population-Based Cohort Study

The aim of this study was to evaluate the influence of I-131 therapy on pregnancy outcome in patients that received therapeutic I-131 doses for thyroid cancer in Taiwan. This nationwide population-based cohort study was based on data from 1998 to 2010 obtained from the Taiwanese National Health Insurance Research Database. We identified 11,708 women with thyroid cancer (≥15 and ≤50 years of age) by International Classification of Diseases, Ninth Revision, Clinical Modification codes. Patients were divided into 2 cohorts: I-131 therapy cohort and non-I-131 therapy cohort. The mean follow-up period was 6.08 years for the I-131 cohort and 6.87 years for the non-I-131 cohort. The case cohort and the control cohort comprised 775 and 716 pregnant patients, respectively. The overall incidence of pregnancy was significantly lower in the I-131 cohort (adjusted HR = 0.77, 95% CI = 0.70–0.86) and it was also observed when the patients were stratified according to age (HR = 0.73, 95% CI = 0.64–0.83 in 25–34 years; HR = 0.63, 95% CI = 0.49–0.82 in 35–44 years). Patients in the I-131 cohort had a lower successful delivery rate, particularly among patients in 25 to 34 years (OR = 0.60, 95% CI = 0.45–0.80). No significant difference was observed for adverse pregnancy conditions between 2 cohorts. I-131 therapy is associated with decreased pregnancy and successful delivery rates. The underlying mechanism likely involves physician recommendation, patient's psychological issue, and potential impact of I-131 treatment on reproductive health. Further investigation is needed.