Objective: To determine between timing and LT4 dose which was the more important factor for IQ at 7 years in screened congenital hypothyroidism (CH). Methods: 131 children with CH born from 1979 to 1994 and 30 controls were studied. Mean age at recall: 22.8 ± 1.1 days. Mean initial LT4: 5.6 ± 0.1 µg/kg/day. Results: Optimal global IQ (GIQ; 119.0 ± 1.8) was obtained for a recall ≤15 days. Results for a recall after 3 weeks were lower (107.7 ± 2.4). The IQ of infants treated before 21 days (117.1 ± 1.2) was identical to the IQ of controls (117.0 ± 2.3) whereas the IQ of those treated after this threshold was lower (108.6 ± 1.7). No significant differences for GIQ were observed with various initial LT4 doses. Infants treated with a dose of LT4 ≧6 µg/kg/day had a higher performance IQ (117.3 ± 1.8 vs. 112.8 ± 1.2) compared with those treated with a dose <6 µg/kg/day. The severity of CH and socio-economic levels were similar in all groups. Conclusion: In this study, timing appears to be the more important factor for the intellectual outcome.

Objective: To study the growth, puberty and compliance of 66 hypothyroid children and to determine prognostic factors for adult height. Patients: 66 children were included (12 boys, 54 girls). Aetiologies were 43 ectopic glands, 14 thyroid agenesis, 9 dyshormonogenesis. Results: In girls the mean adult height was 164.7 ± 6.5 cm for a target height (TH) of 162.8 ± 5.4 cm. In boys the mean adult height was 178.2 ± 6.4 cm for a TH of 175.7 ± 4.7 cm. Puberty development was normal. Children who exceeded their TH had an earlier start of treatment versus children who failed to reach their TH: 24.8 ± 13.5 vs. 42.0 ± 47.3 days, p = 0.004. Delayed normalisation of TSH is a risk factor for bad compliance. Adequate correlations between treatment variables appeared only in children who exceeded their TH. Conclusions: TH, day of start of treatment and compliance with treatment are the main prognostic factors for adult height. Early detection of bad compliance is possible.