Objectives: To study the relationship of 24-hour urinary growth hormone (GH) and IGF-I excretion in childhood to sex and body size. To test the hypothesis that small size at birth followed by postnatal catch-up growth is associated with elevated IGF-I production.
Design and subjects: Follow-up study of a cohort of 183 healthy children born in Salisbury, UK.
Measurements: Weight and height, 24-h urinary growth hormone (uGH) and IGF-I (uIGF-I) excretion, and systolic and diastolic blood pressures.
Results: At 9 years of age, 24-h uIGF-I excretion, but not uGH excretion, was strongly related to current weight (P < 0.001) and height (P < 0. 001). Urinary GH and IGF-I excretion were positively correlated (r = 0.15, P = 0.05). Boys excreted more uIGF-I per unit uGH than girls (uIGF-I/uGH molar ratio 32.1 compared to 21.0; P for difference = 0. 002). There were no significant relationships of uGH, uIGF-I or uIGF-I/uGH molar ratio with birthweight, birthlength or head circumference at birth, nor with blood pressure at 9 years. 'Catch-up' growth, indicated by an increase in height SD scores between birth and 9 years, was associated with higher IGF-I excretion (P = 0.01) and occurred in children with taller parents (P < 0.001).
Conclusions: Boys appear to be more sensitive to GH than girls, generating more uIGF-I in relation to uGH. Urinary IGF-I excretion at 9 years is related to both absolute height and to the degree of catch-up in height from birth. Our results suggest that IGF-I production is strongly influenced by genetic factors, but also by either the degree to which intrauterine growth falls short of genetic growth potential, or the process of postnatal catch-up growth that follows.