Bone Maturation as a Predictive Factor of Catch-up Growth During the First Year of Life in Born Small for Gestational Age Infants: A Prospective Study

Background: About 85-90% of children born small for gestational age (SGA) experience a catch-up growth that occurs mostly during the first year of life and results in a full stature recovery by the age of 2. The remaining 10-15% do not undergo compensatory growth, achieving - if untreated - an adult height approximately 20 cm below their peers. Objective: The aim of this prospective one-center study was to investigate the relation between bone maturation (BM) and catchup growth during the first year of life in SGA infants. Method: Newborns whose weight and/or length was <-2 SD for gestational age were classified as SGA. The study included a group of 32 SGA, 21 of which full-term (37-41 gestation weeks GW, subgroup A1) and 11 preterm (30-36 GW, subgroup A2). Control group (B) consisted of 19 full-term and adequate for gestational age (AGA) newborns. All the partecipants were born in the same hospital and period (2013-2014). Chromosomal disorders, major congenital defects and maternal chronic diseases were criteria of exclusion. The study population underwent longitudinal evaluation of growth parameters and BM at 0, 3, 6 and 12 months. Assessment of BM was performed by ultrasonographyc (US) study of Beclard’s nucleus (<3 mm at birth meaning intrauterine delay of BM). Results: Mean 1st year height velocity (HV) was 25.5±13.2 cm. Significantly higher HV was observed in subgroup A2 versus A1 (32.4±8.0 vs 25.6±2.9 cm, p=0.01); nevertheless, subgroup A2 presented more frequently <-2 SD height outcome at 1 year than subgroup A1 (27.3% vs 0%, p=0.01). If compared with controls, HV was overall higher in SGA group, but without reaching statistical significance (28.6±6.5 vs 25.5±2.9 cm, p=0.10). Intrauterine delay of BM was more common in group A vs B (59.4% vs 21.2%, p=0.0078), and in subgroup A2 vs A1 (90.9% vs 42.9%, p=0.0086). SGA with intrauterine delay of BM showed a constant pattern of catch-up growth, with higher HV and better height gain (29.75±3.1 vs 23.8±2.7 cm, p=0.003) at 12 months evaluation. Conclusion: Our results suggest for the first time that neonatal BM should be regarded as a predictive factor of SGA height gain during the first year of life. US evaluation of Beclard’s nucleus is a useful non–invasive technique to identify intrauterine delay of BM, which can positively influence early postnatal catch-up growth of SGA infants.