Small-for-gestational-age preterm-born infants already have lower bone mass during early infancy.

Abstract

In 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. To 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. In 139 preterm-born infants (51% male, gestational age 30.3±1.5 weeks, birth weight 1341±288g) 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). At 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±10.1g, β=-0.26, 95% CI -0.37; -0.16, p<0.001; six months: 130.1±25.7 versus 145.4±22.9g, 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±20.7g; 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. The 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.