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Low triiodothyronine concentration in preterm infants and subsequent intelligence quotient (IQ) at 8 year follow up

Prematurity is associated with clinically important changes in endocrine physiology. We have reported reduced plasma concentrations of many hormones in premature compared with full term infants, including prolactin,1 testosterone,2 and, notably, triiodothyronine.3 Thyroid hormones are critical signals for brain development.4 We showed a reduction of 7-9 points in scores in standardised mental and motor development tests at 18 months of age in preterm infants, even after adjustment for potential confounding factors.3 As cognitive function at 18 months may not reflect later intelligence quotient (IQ), we measured IQ in the same group of preterm infants 7.5-8 years later when scores are likely to reflect adult values.

We measured plasma triiodothyronine concentrations longitudinally in 279 infants in samples taken at 1-3 …