Congenital Hypothyroidism: Decreased Growth Velocity in the First Weeks of Life

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Abstract
The growth velocity of 46 infants with congenital hypothyroidism, classified into three groups: athyreosis (n = 12), ectopic (n = 25) and eutopic gland (n = 9), was analyzed. Height, expressed as the standard deviation score (SDS), was measured at birth, at diagnosis and 2, 4, and 8 weeks after initiation of therapy. Bone age was retarded at birth and at diagnosis, epiphyseal surfaces of the knee were correlated with serum T4 values. By contrast, height (mean ± SD) at birth was normal (0.3 ± 0.8 SDS) with identical distribution among the three subgroups. Growth velocity was decreased during the first weeks of life: height at diagnosis was -0.1 ± 0.6 SDS, a value significantly different from size at birth (p < 0.02). After therapy was started, a continuous decline in rowth velocity was observed, reaching-0.2 ± 0.7 and -0.2 ± 0.6 SDS, respectively, at 2 and 4 weeks of therapy (p < 0.01 vs. size at birth). Growth retardation was correlated with the degree of thyroid deficiency. Mean height after 2 weeks of therapy was at -0.6, -0.1 0.1 SDS in patients with athyreosis, ectopic and eutopic gland, respectively. Catch-up growth occurred thereafter, and the mean height reached 0.3 SDS at 12 weeks for the entire group. A correlation between the decrease in growth velocity and T4 levels at diagnosis was found (p < 0.05). The normal size at birth and the decreased growth rate observed at diagnosis seem to indicate that growth becomes thyroid hormone dependent immediately after birth.