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

Abstract

Background: 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.

Objective: 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.

Design: 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).

Results: 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.

Conclusion: 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.