Objective: The aim of this study was to calculate the embryo/fetus dose in pregnant patients who have accidentally received radioiodine (131I) and to evaluate the termination of pregnancy by giving teratological advice to the family.

Methods: In this study, fetus dose was calculated in 16 patients who were referred to our department following the application of 131I radioisotope for diagnosis and treatment in different nuclear medicine centers.

Results: Mean embryo/fetus dose of three pregnant patients, who received 0.37 MBq (10 μCi) 131I orally for thyroid uptake test, was calculated as 0.063 mGy. For uptake/scintigraphy test, 1.85 MBq (0.05 mCi) 131I was applied to six patients, and the calculated mean fetal dose was 0.13 mGy and fetal thyroid dose was 1073 mGy (1.073 Gy). Mean embryo/fetus dose of three patients who received mean 185 MBq (5 mCi) 131I orally for whole body scintigraphy was calculated as 13.2 mGy. One of two patients with hyperthyroidism was administered 370 MBq (10 mCi) 131I orally and the embryo/fetus dose was calculated as 26.64 mGy and fetal thyroid dose was calculated as 215340 mGy (215.34 Gy). The other patient with hyperthyroidism received 481 MBq (13 mCi) 131I and embryo/fetus dose was calculated as 34.63 mGy. One of two patients diagnosed with thyroid cancer received 3700 MBq (100 mCi) 131I and the embryo/fetus dose was calculated as 266.64 mGy. The other patient with thyroid cancer received 5555 MBq (150 mCi) 131I at 15th gestational week, and fetus dose was calculated as 377.8 mGy and fetal thyroid dose was calculated as 3221.9 Gy.

Conclusion: Diagnostic 131I administration before the 10th week of pregnancy induces insufficient radiation dose for termination of pregnancy. Whilst, the embryo/fetus dose in pregnant women with high doses of 131I rise up to more than 100 mGy and these cases shoulde be therefore evaluated in terms of termination of pregnancy.