Preterm Children Born Small for Gestational Age are at Risk for Low Adult Bone Mass

Cross-sectional studies suggest that premature birth and low birth weight may both be associated with low peak bone mass. We followed bone traits in preterm individuals and controls for 27 years and examined the effects of birth weight relative to gestational age [stratified as small for gestational age (SGA) or appropriate for gestational (AGA)] on adult bone mineral density (BMD). We measured distal forearm BMC (g/cm) and BMD (g/cm²) with single-photon absorptiometry (SPA) in 46 preterm children (31 AGA and 15 SGA) at mean age 10.1 years (range 4–16) and in 84 healthy age-matched children. The measurements were repeated 27 years later with the same SPA apparatus but then also with dual energy absorptiometry and peripheral computed tomography (pQCT). Preterm individuals were shorter (p = 0.03) in adulthood than controls. Preterm AGA individuals had similar BMC and BMD height-adjusted Z-scores in adulthood compared to controls. Preterm SGA individuals had lower distal forearm BMC and BMD height-adjusted Z-scores in adulthood than both controls and preterm AGA individuals. Preterm SGA individuals had lower gain from childhood to adulthood in distal forearm BMC height-adjusted Z-scores than controls (p = 0.03). The deficits in preterm SGA individuals in adulthood were also captured by DEXA in height-adjusted femoral neck (FN) BMC Z-score and height-adjusted FN BMD Z-score and by pQCT in tibial cross-sectional area (CSA) Z-score and stress strain index (SSI) Z-score, where all measurements were lower than controls (all p values <0.05). Preterm SGA individuals are at increased risk of reaching low adult bone mass, at least partly due to a deficit in the accrual of bone mineral during growth. In our cohort, we were unable to find a similar risk in preterm AGA individuals.