Study designs of evaluations included in the review
Cohort studies. The between-study comparison required studies of children with congenital hypothyroidism, as identified by neonatal screening, whose global or cognitive development had been assessed using a population-standardised measure. The within-study comparison required cohort studies of children with congenital hypothyroidism, as identified by neonatal screening, and had to include an analysis of either of the following: the relationship between starting dose and any measure of global or cognitive development or growth, adjusted for severity of hyperthyroidism at diagnosis on the basis of serum T4 levels or bone age; the relationship between starting dose and any measure of behaviour.
Specific interventions included in the review
Studies investigating children with congenital hypothyroidism, as identified by neonatal screening, who were receiving a starting dose of levothyroxine.
Participants included in the review
Children with congenital hypothyroidism, as identified by neonatal screening, whose global or cognitive development had been assessed using a population-standardised measure. The children included in the review were aged between 1 and 14 years.
Outcomes assessed in the review
First, the authors compared standardised doses of levothyroxine treatment with the mean standardised development scores in cohorts with different starting doses of levothyroxine. Second, the authors sought studies that compared development growth or behaviour in children treated with different starting doses of levothyroxine within the cohort. The studies included in the within-study comparison had to address the potential confounding effects of severity of hypothyroidism at diagnosis.
How were decisions on the relevance of primary studies made?
Two independent reviewers determined whether the studies met the inclusion criteria.