Does undergoing radioactive iodine-131 (I-131) treatment before marriage affect fertility?

Thyroid iodine-131 (I-131) scanning involves oral administration of I-131 on an empty stomach. After absorption through the gastrointestinal tract, the radioactive isotope enters the bloodstream and is rapidly taken up by thyroid follicular epithelial cells. The amount and rate of uptake are closely correlated with thyroid function.

Unmarried women may undergo I-131 scanning, except in special circumstances.

Iodine-131 is a radioactive substance that, like dietary iodine, participates in thyroid hormone synthesis. When thyroid cells or differentiated thyroid cancer cells absorb I-131, the emitted radiation destroys these cells—thereby achieving therapeutic effects.

Iodine accumulates predominantly within the thyroid gland. Moreover, the beta particles emitted by I-131 have a very short tissue penetration range—only about 2 mm—resulting in minimal radiation exposure and damage to surrounding tissues. Thus, I-131 therapy offers highly targeted and precise treatment. It is particularly effective—and considered the first-line treatment—for hyperthyroidism and thyroid cancer, while sparing adjacent healthy tissues.

During I-131 therapy, the gonads receive some degree of radiation exposure, and pre-treatment hypothyroidism may affect fertility and treatment outcomes. Therefore, it is generally recommended to wait at least six months after I-131 therapy before attempting pregnancy. During pregnancy, aside from appropriate dose adjustments of thyroid hormone replacement medication, management is otherwise identical to that for non-pregnant women.