Abstract
Radioactive iodine (131I) 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 131I 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 131I 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 131I need to be aware of the risks of in utero 131I 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 131I 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 131I.
Abbreviations:
MR (mental retardation), CNS (central nervous system), TSH (thyroid stimulating hormone), IQ (intelligence quotient), ICRP (International Commission on Radiological Protection), hCG (human chorionic gonadotropin)Keywords
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Article info
Publication history
Published online: February 06, 2021
Accepted:
February 3,
2021
Received in revised form:
January 27,
2021
Received:
November 10,
2020
Identification
Copyright
© 2021 Elsevier B.V. All rights reserved.
