Bone maturation in extremely low birth weight infants in relation to birth weight and endocrine parameters

Modern intensive care techniques have led to higher survival rates of extremely low birth weight infants (ELBW, birth weight <1,000 g). Previous studies have suggested a link between abnormal birth parameters and subsequent endocrine disturbances, but a possible impact on bone maturation during childhood has not been studied. ELBW children were studied (mean chronological age (CA), 6.01 years; range, 4.5–8.2). Skeletal maturation was assessed according to Greulich and Pyle (8). Bone age (BA) was defined as retarded when ΔBA-CA was < −1 SD and accelerated when ΔBA-CA was >+1 SD. BA was either retarded or accelerated in 15 patients (24.6%). Twenty-one of 61 radiograms (34.4%) showed a discordant BA with a marked gender difference (14/24 boys; 7/37 girls). ΔBA-CA correlated significantly with BMI (r = 0.36; p = 0.005) and height SDS (r = 0.35; p = 0.006). We found significant correlations between BA and androgens. Insulin-like growth factor binding protein-1 (IGFBP-1), which decreases in insulin-resistant individuals, correlated negatively with BA. In conclusion, bone maturation in ELBW children is correlative with height and weight. It is modulated by a variety of metabolic factors, including IGFBP-1 and androgens. Bone age, together with height and weight catch-up, can thus possibly serve as early indicators of insulin resistance later in life.