Effect of Different Starting Doses of Levothyroxine on Growth and Intellectual Outcome at Four Years of Age in Congenital Hypothyroidism

To evaluate the effect of different initial levothyroxine (LT4) replacement doses on growth and intellectual outcome in patients with congenital hypothyroidism (CH) detected by neonatal screening program, the longitudinal growth and intelligence quotient (IQ) were assessed and compared at 4 years of age in 83 patients with CH. The patients were divided into three groups according to the initial LT4 dose used: (1) group 1 (n = 42) received the previously recommended dose of 6.0-8.0 μg/kg per day; (2) group 2 (n = 21) received a dose of 8.1-10.0 μg/kg per day; (3) Group 3 (n = 20) a dose of 10.1-15.0 μg/kg per day. The IQ, evaluated by the Wechsler Preschool and Primary Scale of Intelligence test at 4 years of age, was significantly higher in group 3 (IQ 98 ± 9) compared to group 1 (IQ 88 ± 13; p < 0.05) but not compared to group 2 (IQ 94 ± 13). However, the IQs were below the normal range (< 85) in six patients from group 2 (28%), but in none of the patients from group 3 (p = 0.03). Patients from group 3, ...