A Cochrane review included 1 study with a total of 47 babies. The study investigated the effects of high versus low dose thyroid hormone replacement in relation to time taken to achieve euthyroid status and neurodevelopmental outcome (follow-up between 21 months and 8 years of age; 16 children were lost to follow-up). A high dose was more effective in rising serum thyroxine and free thyroxine concentrations to the target range and earlier normalisation of thyroid stimulating hormone compared to a lower dose. Participants who were on higher initial dose of 50 mcg/day L-thyroxine had higher full scale intelligence quotient (IQ) scores compared to participants who were on lower initial dose of 37.5mcg/day. Verbal IQ, performance IQ and achievement scores did not differ among the three groups. Growth and adverse effects were not reported in the included trial.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment, unclear blinding, and more than 20% loss to follow-up), and by imprecise results (limited study size for each comparison).