Thyroid nodules after prenatal exposure to chernobyl radioactive fallout in Belarus

To assess the risk of thyroid nodules associated with prenatal radiation exposure. Thyroid screening was conducted among 1,439 Belarusians who were prenatally exposed to radioactive fallout from the Chernobyl nuclear plant accident. Estimated thyroid doses (mean, 0.14; median, 0.02 gray [Gy]) were predominately from intake of 131I. Binary logistic regression models were used to estimate excess odds ratios (EORs) for thyroid nodules associated with radiation dose. A total of 258 screening participants had one or more nonneoplastic thyroid nodules. Among all participants, there was a linear dose response with an EOR/Gy of 0.44 (95% CI: −0.01, 1.38) of borderline significance (p = .06). This was driven by a significant EOR/Gy of 0.84 (95% CI: 0.07, 2.45; p = .02) among participants who were in the third trimester at the time of the accident (ATA). No significant associations with radiation were found among those who were in the second or first trimester ATA, but there were considerable uncertainties. No significant differences in dose response were found by nodule size or multiplicity. The significant risk of thyroid nodules associated with exposure in the third trimester indicates the presence of a vulnerable subgroup of pregnant women at the time of an accidental radioiodine release. Because of the strong correlation between gestational age and 131I dose in the fetal thyroid, the extent to which this excess risk is attributable to elevated 131I dose and/or radiosensitivity of the thyroid in later stage of fetal development remains unclear.