Original Full Length ArticleSmall-for-gestational-age preterm-born infants already have lower bone mass during early infancyâ˜

BackgroundIn preterm-born infants, low birth weight and diminished bone accretion deteriorate peak bone mass. Whether low birth weight is already associated with decreased bone mass during infancy is unknown.ObjectiveTo study the effect of birth weight on bone accretion between term age (40 weeks postmenstrual age) and six months post-term in preterm-born infants.DesignIn 139 preterm-born infants (51% male, gestational age 30.3 ± 1.5 weeks, birth weight 1341 ± 288 g) weight and whole-body bone mineral content (BMC, gram) were measured at term age and six months post-term. At birth, infants were small-for-gestational-age (SGA, n = 33, weight and/or length < − 2 SDS) or appropriate-for-gestational-age (AGA, n = 98, weight and length ≥ − 2 SDS).ResultsAt term age and six months post-term, BMC adjusted for gender and gestational age was lower in SGA than AGA infants (term age: 38.1 ± 9.5 versus 48.6 ± 10.1 g, β = − 0.26, 95% CI − 0.37; − 0.16, p < 0.001; six months: 130.1 ± 25.7 versus 145.4 ± 22.9 g, β = − 0.16, 95% CI − 0.25; − 0.08, p < 0.001). At six months post-term, BMC remained lower in SGA infants after adjustment for actual weight and length. Between term age and six months post-term, BMC gain adjusted for gender and gestational age was lower in SGA than AGA infants (91.7 ± 22.8 versus 98.2 ± 20.7 g; β = − 0.12, 95% CI − 0.24; − 0.003, p = 0.044). BMC gain remained lower in SGA infants after adjustment for weight and length gain.ConclusionThe first six months post-term, SGA preterms have lower bone accretion, independent of body size, suggesting that prenatal conditions for bone accretion cannot be replicated postnatally.

► The effect of birth weight on post-term bone accretion was studied in preterm-born infants. ► Small-for-gestational-age preterm-born infants have lower post-term bone mass, independent of body size, skeletal size and type of feeding. ► The prenatal growth trajectory appears to be the main determinant of bone mass accretion in preterm-born infants. ► The postnatal environment cannot replicate the favorable intra-uterine conditions for bone mass accretion in preterm-born infants.