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Women with high early pregnancy urinary iodine levels have an increased risk of hyperthyroid newborns: the population‐based G eneration R S tudy
Author(s) -
Medici Marco,
Ghassabian Akhgar,
Visser Willy,
Muinck KeizerSchrama Sabine M. P. F.,
Jaddoe Vincent W. V.,
Visser W. Edward,
Hooijkaas Herbert,
Hofman Albert,
Steegers Eric A. P.,
BongersSchokking Jacoba J.,
Ross H. Alec,
Tiemeier Henning,
Visser Theo J.,
Rijke Yolanda B.,
Peeters Robin P.
Publication year - 2014
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/cen.12321
Subject(s) - iodine , medicine , thyroid function , endocrinology , population , urinary system , iodine deficiency , pregnancy , thyroid , chemistry , biology , environmental health , organic chemistry , genetics
Objective Iodine deficiency during pregnancy results in thyroid dysfunction and has been associated with adverse obstetric and foetal effects, leading to worldwide salt iodization programmes. As nowadays 69% of the world's population lives in iodine‐sufficient regions, we investigated the effects of variation in iodine status on maternal and foetal thyroid (dys)function in an iodine‐sufficient population. Design, Participants and Measurements Urinary iodine, serum TSH , free T4 ( FT 4) and TPO ‐antibody levels were determined in early pregnancy (13·3 (1·9) week; mean ( SD )) in 1098 women from the population‐based G eneration R S tudy. Newborn cord serum TSH and FT 4 levels were determined at birth. Results The median urinary iodine level was 222·5 μg/l, indicating an iodine‐sufficient population. 30·8% and 11·5% had urinary iodine levels <150 and >500 μg/l, respectively. When comparing mothers with urinary iodine levels <150 vs ≥150 μg/l, and >500 vs ≤500 μg/l, there were no differences in the risk of maternal increased or decreased TSH , hypothyroxinaemia or hyperthyroidism. Mothers with urinary iodine levels >500 μg/l had a higher risk of a newborn with decreased cord TSH levels (5·6 ± 1·4 (mean ± SE ) vs 2·1 ± 0·5%, P = 0·04), as well as a higher risk of a hyperthyroid newborn (3·1 ± 0·9 vs 0·6 ± 0·3%, P = 0·02). These mothers had newborns with higher cord FT 4 levels (21·7 ± 0·3 vs 21·0 ± 0·1 p m , P = 0·04). Maternal urinary iodine levels <150 μg/l were not associated with newborn thyroid dysfunction. Conclusions In an iodine‐sufficient population, higher maternal urinary iodine levels are associated with an increased risk of a hyperthyroid newborn.