Iijima Shigeo
Department of Regional Neonatal-Perinatal Medicine, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu, Shizuoka, 431-3192, Japan.
Eur J Obstet Gynecol Reprod Biol. 2021 Apr;259:53-59. doi: 10.1016/j.ejogrb.2021.02.003. Epub 2021 Feb 6.
Radioactive iodine (I) therapy is absolutely contraindicated in pregnancy, but reports of inadvertent exposure continue to appear in the literature. Radiation-induced effects on the embryo/fetus are highly dependent on the stage of pregnancy, the dose absorbed by the embryo/fetus, and the manifestations of the pathological condition that develops as a result of the irradiation. Prior to implantation, the major concern is death of the embryo when exposed to radiation greater than the 100 mGy threshold. At this very early stage of pregnancy, exposure to I is unlikely to cause major malformations or thyroid dysfunction in surviving embryos. Exposure during organogenesis of the thyroid (from 10 weeks of gestation onward) and that of other organs at radiation thresholds of 100-300 mGy may result in fetal thyroid ablation, malformations, growth restriction, and in later life, mental retardation (MR). In addition, any dose of radiation exposure may increase the risk of cancer many years after the in utero exposure. Fetal and neonatal hypothyroidism due to in utero I exposure may require lifelong thyroxine replacement therapy and result in severe MR if the condition is not recognized immediately. Therefore, thyroid function must be evaluated and replacement therapy should be started without delay even before birth. Physicians treating women of childbearing age with I need to be aware of the risks of in utero I exposure and take all measures to avoid inadvertent exposure during pregnancy. Nevertheless, in case of accidental exposure, the clinician should confirm the gestational age at exposure, evaluate the risks to the fetus by estimating the radiation dose delivered, and discuss the subsequent management plan with the pregnant woman. This review aimed to summarize the current knowledge regarding the risk of harm to the developing fetus after in utero I exposure, especially focusing on the effects on thyroid function. This study also evaluated the most significant new findings regarding the prevention and in utero and peripartum management of fetal exposure to I.
放射性碘（I）治疗在孕期绝对禁忌，但文献中仍不断有意外暴露的报道。辐射对胚胎/胎儿的影响高度依赖于孕期阶段、胚胎/胎儿吸收的剂量以及辐射导致的病理状况的表现。在着床前，主要担忧的是胚胎暴露于大于100 mGy阈值的辐射时死亡。在妊娠这个非常早期的阶段，暴露于碘不太可能在存活的胚胎中导致严重畸形或甲状腺功能障碍。在甲状腺器官形成期（从妊娠10周起）以及其他器官在100 - 300 mGy辐射阈值下暴露，可能导致胎儿甲状腺消融、畸形、生长受限，以及在以后的生活中出现智力发育迟缓（MR）。此外，任何剂量的辐射暴露都可能在子宫内暴露多年后增加患癌风险。由于子宫内碘暴露导致的胎儿和新生儿甲状腺功能减退可能需要终身甲状腺素替代治疗，如果病情未立即被识别，可能会导致严重的智力发育迟缓。因此，即使在出生前也必须立即评估甲状腺功能并开始替代治疗。用碘治疗育龄妇女的医生需要意识到子宫内碘暴露的风险，并采取一切措施避免孕期意外暴露。然而，万一发生意外暴露，临床医生应确认暴露时的孕周，通过估计所传递的辐射剂量评估对胎儿的风险，并与孕妇讨论后续的管理计划。本综述旨在总结目前关于子宫内碘暴露后对发育中胎儿造成伤害风险的知识，尤其关注对甲状腺功能的影响。本研究还评估了关于预防以及胎儿暴露于碘后的子宫内和围产期管理的最重要新发现。
