Objective: Birth weight influences both postnatal growth and the initial response to GH therapy in GH-deficient subjects, but its relationship to final height is uncertain. Therefore, we examined final height results in a group of subjects treated for GH deficiency who were born small, appropriate or large for gestational age (GA).
Design: Retrospective study.
Patients: 108 GH-treated patients (age at diagnosis 11.1 +/- 2.0 years) affected by idiopathic and isolated GH deficiency (peak < 8 microg/l after pharmacological and/or nocturnal mean GH concentration </= 3.3 microg/l) were examined. Twenty-four had a birth weight < 3rd centile (2300 g +/- 268 - small for GA), 77 between the 3rd and 90th centile (3216 g +/- 317: appropriate for GA) and 7 above the 90th centile (4193 g +/- 143: large for GA).
Measurements: All subjects reached final height (growth velocity < 0.5 cm/year in the last year of treatment) after hGH treatment (range 33-96 months) at a dose of 20 U/m2/week. The 3 groups of subjects started therapy at a similar height for chronological and bone age.
Results: Final height in the small for GA group was - 1.71 +/- 0.93 standard deviation score (SDS), significantly lower than that of both appropriate (- 1.14 +/- 0.83 (P < 0.01)) and large (- 0.70 +/- 0.89 (P < 0.01)) for GA groups. Similarly, the small for GA group had a significantly lower height SDS increment from the start of therapy to adult height (0.54 +/- 0.84) than both the appropriate (0.99 +/- 0.78 (P < 0.05)) and the large (1.49 +/- 0.84 (P < 0.01)) for GA groups. The percentage of subjects with final height above target height was significantly different in the 3 groups: 21% for the small, 38% for the appropriate and 71% for the large for GA groups (P < 0.05). In the whole group of patients there was a positive correlation between birth weight and final height (r = 0.38; P < 0.0001).
Conclusions: The present study showed that our patients, affected by isolated and idiopathic GH deficiency but with different birth weights, despite starting treatment with a similar height and bone age delay, had different auxological outcomes. It seems, therefore, that final height is strongly influenced by birth weight which penalizes the smaller newborns and assists the larger ones.