Transient hypothyroxinemia in preterm infants: the role of cord sera thyroid hormone levels adjusted for prenatal and intrapartum factors

Fiona L. R. Williams, Gary J. Mires, Carol Barnett, Simon A. Ogston, Hans van Toor, Theo J. Visser, Robert Hume, Scottish Preterm Thyroid Group

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    Abstract

    Context: Transient hypothyroxinemia is common in infants less than 30 wk gestation and is associated with neurodevelopmental deficits; it has no consensus definition. We previously suggested that appropriate ranges for postnatal serum T-4 values are at least cord levels corrected to an equivalent gestational age if the fetuses had remained in utero.

    Objective: The study objective is to investigate the contribution of prenatal and intrapartum factors (n = 27) to the variations in cord levels of iodothyronines, T-4-binding globulin, and TSH, and to provide an appropriate definition of transient hypothyroxinemia.

    Design: The study design is a cohort study (n = 620) in 11 Scottish neonatal intensive care units.

    Patients: Infants were delivered at 23- to 42-wk gestation and recruited between January 1998 and September 2001.

    Results: Using -2 SD of adjusted T-4 cord levels applied to postnatal d-7 values of equivalent gestational age, 14% of the 23- to 27-wk group, 1% of the 28- to 30-wk group, and 3% of the 31- to 34-wk group are hypothyroxinemic; using -1 SD, the respective figures are 41, 23, and 12%.

    Conclusions: In the absence of neurodevelopmental follow-up studies to quantify transient hypothyroxinemia, a pragmatic criterion is necessary for selection of extreme preterm infants into clinical trials of T-4 supplementation. We suggest the use of serum T-4 levels on postnatal d 7 that are below -1 SD of adjusted cord T-4 levels of equivalent gestational age. This criterion avoids overrecruitment of the more mature infants in whom universal T-4 supplementation is detrimental to neurodevelopmental outcome, but still allows selection of the least mature entrants on whom universal T-4 supplementation is beneficial.

    Original languageEnglish
    Pages (from-to)4599-4606
    Number of pages8
    JournalJournal of Clinical Endocrinology & Metabolism
    Volume90
    Issue number8
    DOIs
    Publication statusPublished - Aug 2005

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