Objectives Postnatal thyroid dysfunction is common in preterm infants but the relationship between mild dysfunction and neurodevelopment is unclear. Our aim is to describe the relationship between thyroid function and neurodevelopment.
Design Cohort analysis.
Patients 1275 infants born under 31 weeks’ gestation; there were no exclusion criteria.
Setting The infants were part of a UK daily iodine supplementation trial.
Main outcomes Thyroid-stimulating hormone, thyroid-binding globulin and total thyroxine levels were measured in dried blood spots on postnatal days 7, 14, 28 and the equivalent of 34 weeks’ gestation. Neurodevelopment was measured using the Bayley-III Scales of infant development at 2 years of age.
Results No infant was identified as hypothyroid through routine screening. The 3% of infants consistently in the top decile of gestationally age-adjusted thyroid-stimulating hormone levels had a reduction in cognitive score of 7 Bayley units when compared with those not in the top decile (95% CI –13 to –1). A reduction in motor composite score of 6 units (95% CI −12 to <−0.1) and fine motor score of 1 unit (95% CI –2 to –0.1) was also identified. The 0.7% of infants consistently in the bottom decile of age-adjusted thyroxine levels had a reduction in motor composite score of 14 units (95% CI –25 to –2) and its two subset scores, fine and gross motor, of 2 units (95% CI respectively −4.5 to <−0.1 and –4.3 to –0.3).
Conclusions Preterm infants with consistent ‘mild’ thyroid dysfunction score less on neurodevelopmental tests at 2 years of age. Many of these infants will not be detected by current clinical protocols or screening programmes.
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Contributors FLRW: conceptualised and designed the study, designed and contributed to the data analysis, drafted the initial manuscript and approved the final manuscript as submitted. AL: contributed to the study design, critically reviewed the manuscript and approved the final manuscript as submitted. JW: contributed to the data analysis, reviewed and revised the manuscript and approved the final manuscript as submitted. AB: coordinated and supervised the analysis of blood spot cards, critically reviewed the manuscript and approved the final manuscript as submitted. TC: contributed to the design of the data analysis, reviewed and revised the manuscript and approved the final manuscript as submitted.
Funding This study was funded by Medical Research Council (UK) and managed by NIHR on behalf of the MRC-NIHR partnership.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval The trial was approved by Tayside Committee on Medical Research Ethics (08/S0501/31).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data may be obtained from a third party and are not publicly available. De-identified participant data will be shared in accordance with the National Perinatal Epidemiology Unit Data Sharing policy and Nuffield Department of Population Health Data Sharing policy. Requests for access to the data will be considered by the National Perinatal Epidemiology Unit Data Sharing committee from the date of publication. Data will be shared after approval of a proposal with investigator approval and completion of a signed data sharing agreement. Access to the data can be requested from email@example.com.