Clinical Endocrinology

Women with high early pregnancy urinary iodine levels have an increased risk of hyperthyroid newborns: the population-based Generation R Study

Authors

  • Marco Medici,

    1. The Generation R Study Group, Erasmus Medical Center, The Netherlands
    2. Department of Internal Medicine, Erasmus Medical Center, The Netherlands
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  • Akhgar Ghassabian,

    1. The Generation R Study Group, Erasmus Medical Center, The Netherlands
    2. Department of Child and Adolescent Psychiatry, Erasmus Medical Center – Sophia Children's Hospital, The Netherlands
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  • Willy Visser,

    1. Department of Obstetrics and Gynecology, Erasmus Medical Center – Sophia Children's Hospital, The Netherlands
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  • Sabine M. P. F. de Muinck Keizer-Schrama,

    1. Department of Endocrinology, Erasmus Medical Center – Sophia Children's Hospital, The Netherlands
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  • Vincent W. V. Jaddoe,

    1. The Generation R Study Group, Erasmus Medical Center, The Netherlands
    2. Department of Pediatrics, Erasmus Medical Center – Sophia Children's Hospital, The Netherlands
    3. Department of Epidemiology, Erasmus Medical Center, The Netherlands
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  • W. Edward Visser,

    1. Department of Internal Medicine, Erasmus Medical Center, The Netherlands
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  • Herbert Hooijkaas,

    1. Department of Immunology, Erasmus Medical Center, Rotterdam, The Netherlands
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  • Albert Hofman,

    1. Department of Epidemiology, Erasmus Medical Center, The Netherlands
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  • Eric A. P. Steegers,

    1. Department of Obstetrics and Gynecology, Erasmus Medical Center – Sophia Children's Hospital, The Netherlands
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  • Jacoba J. Bongers-Schokking,

    1. Department of Endocrinology, Erasmus Medical Center – Sophia Children's Hospital, The Netherlands
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  • H. Alec Ross,

    1. Department of Laboratory Medicine, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
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  • Henning Tiemeier,

    1. Department of Child and Adolescent Psychiatry, Erasmus Medical Center – Sophia Children's Hospital, The Netherlands
    2. Department of Epidemiology, Erasmus Medical Center, The Netherlands
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  • Theo J. Visser,

    1. Department of Internal Medicine, Erasmus Medical Center, The Netherlands
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  • Yolanda B. de Rijke,

    1. Department of Internal Medicine, Erasmus Medical Center, The Netherlands
    2. Department of Clinical Chemistry, Erasmus Medical Center – Sophia Children's Hospital, Rotterdam, the Netherlands
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  • Robin P. Peeters

    Corresponding author
    1. Department of Internal Medicine, Erasmus Medical Center, The Netherlands
    • Correspondence: Robin P. Peeters, Room D 430, Department of Internal Medicine, Erasmus Medical Center, Dr Molewaterplein 50, 3015 GE, Rotterdam, the Netherlands. Tel.: +31 10 4635463; Fax: +31 10 7035430; E-mail: r.peeters@erasmusmc.nl

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Abstract

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 (FT4) and TPO-antibody levels were determined in early pregnancy (13·3 (1·9) week; mean (SD)) in 1098 women from the population-based Generation R Study. Newborn cord serum TSH and FT4 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%, = 0·04), as well as a higher risk of a hyperthyroid newborn (3·1 ± 0·9 vs 0·6 ± 0·3%, = 0·02). These mothers had newborns with higher cord FT4 levels (21·7 ± 0·3 vs 21·0 ± 0·1 pm,= 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.

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