Hamada K, Mizokami T, Maruta T, Higashi K, Konishi K, Momotani N, Tajiri J. Thyroid Function of Infants Breastfed by Mothers with Graves Disease Treated with Inorganic Iodine: A Study of 100 Cases.
J Endocr Soc 2021;
5:bvaa187. [PMID:
33381674 PMCID:
PMC7757433 DOI:
10.1210/jendso/bvaa187]
[Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Indexed: 11/19/2022] Open
Abstract
Context
We previously reported that inorganic iodine therapy in lactating women with Graves disease (GD) did not affect the thyroid function in 25 of 26 infants despite their exposure to excess iodine via breast milk.
Objective
To further assess thyroid function in infants nursed by mothers with GD treated with inorganic iodine.
Design
Case series
Setting
Tajiri Thyroid Clinic, Japan
Participants
One hundred infants of lactating mothers with GD treated with potassium iodide (KI) for thyrotoxicosis
Main Outcome Measures
Infant blood thyrotropin (TSH) and free thyroxine (FT4) levels were measured by the filter paper method. Subclinical hypothyroidism was defined as TSH ≥10 μIU/mL and ≥5 μIU/mL in infants aged <6 and ≥6 months, respectively.
Results
Overall, 210 blood samples were obtained from 100 infants. The median infant age was 5 (range, 0-23) months; median maternal KI dose, 50 (4-100) mg/day; median blood TSH level, 2.7 (0.1-12.3) μIU/mL; and median blood FT4 level, 1.04 (0.58-1.94) ng/dL. Blood TSH level was normal in 88/100 infants. Twelve infants had subclinical hypothyroidism; among them, blood TSH levels normalized after maternal KI withdrawal or stopping breastfeeding in 3 infants. In 7 infants, blood TSH levels normalized during KI administration without stopping breastfeeding. Two infants could not be followed up.
Conclusion
In Japan, inorganic iodine therapy for lactating women with GD did not affect thyroid function in most of the infants. Approximately 10% of infants had mild subclinical hypothyroidism, but blood TSH level normalized during continued or after discontinuing iodine exposure in all followed up infants.
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