MON-401 - Risk Factors for Reproductive and Gonadal Adverse Effects after Radioactive Iodine for Differentiated Thyroid Cancer: A Scoping Review

Background: Radioactive iodine (RAI) is commonly used in differentiated thyroid cancer (DTC), including in patients of reproductive age. Although overall reproductive outcomes are often considered reassuring, risk appears heterogeneous, and factors associated with reproductive and gonadal adverse effects remain poorly defined, limiting individualized counseling.

Methods: We conducted a registered PRISMA-ScR–guided scoping review to map patient-, disease-, and treatment-related risk factors for reproductive and gonadal adverse effects after RAI in adults with DTC, including endocrine preparation and suppression strategies where relevant. MEDLINE, Embase, and Cochrane were searched (2011–2025). Two reviewers screened 7,184 records and assessed 604 full texts. Studies reporting risk factor–outcome associations were summarized descriptively and categorized by direction and consistency.

Results: Among 114 included studies (n=107,742), only 12 evaluated reproductive or gonadal outcomes, revealing distinct sex-specific risk patterns. In women, ovarian reserve measures, most commonly anti-Müllerian hormone (AMH), demonstrated the most consistent vulnerability signal, with age and reproductive stage emerging as important effect modifiers across studies. Associations between administered RAI activity and ovarian reserve were heterogeneous, with mixed dose–response findings. Menstrual outcomes were inconsistently associated with RAI activity. Pregnancy outcomes indicated that reproductive timing and maternal age were more influential than RAI activity. Conception within several months of RAI was associated with congenital malformations, whereas delayed conception (≥24 months) was associated with preterm delivery; RAI activity was not independently associated. In men, treatment intensity was more consistently associated with risk: multiple treatments and higher administered activity were linked to transient spermatogenic impairment, including reduced sperm concentration and elevated follicle-stimulating hormone, with partial or complete recovery within months to one year.

Conclusions: Despite limited and heterogeneous evidence, consistent sex-specific patterns of reproductive and gonadal risk after RAI in DTC emerge. Female risk appears most strongly modified by age and reproductive timing rather than administered activity, whereas male risk is more consistently associated with treatment intensity and cumulative exposure. These findings support sex-specific fertility counseling and highlight the need for standardized outcome definitions, longer follow-up, and risk-focused studies incorporating endocrine preparation and suppression strategies to enable individualized counseling and clinically actionable risk prediction.

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