Preterm birth and risk of bone fractures during childhood and early adulthood.

People born preterm have reduced BMD, subnormal peak bone mass, and an increased risk of osteoporosis. Whether this translates to increased risk of bone fractures is uncertain. We assessed fracture risk from childhood to early adulthood in relation to gestational age and sex by conducting a nationwide register-linkage cohort study comprising all 223 615 liveborn (January 1987-September 1990) singletons (9161, 4.1%; preterm) in Finland. Cox regression models provided hazard ratios (HRs) for fracture diagnosis in public specialty health care in both first and recurrent event settings during the whole follow-up (0-29 years) and during different age periods (0-4, 5-9, 10-29 years). Gestational age was considered categorical (full-term, 39-41 weeks; reference). A total of 39 223 (17.5%) children or young adults had at least 1 fracture. In analyses not stratified by sex, only extremely preterm birth (<28 completed weeks' gestation) was associated with risk of bone fracture at 0-29 years (adjusted HR [aHR]: 0.46; 95% CI: 0.28-0.74) compared with those born full-term. Among females, gestational age was unrelated to fracture risk at 0-29 years. Among males, extremely and very preterm (28-31 weeks) birth was associated with lower risk of fracture at 0-29 years compared with those born full-term (aHR: 0.38 [95% CI: 0.21-0.71] and 0.75 [95% CI: 0.59-0.95], respectively). Restricting the analyses to the individuals without severe medical condition(s) attenuated the associations. However, the fracture risk varied according age and sex: at 10-29 years, moderately preterm (32-33 weeks) females and extremely and very preterm males had a lower risk (aHR: 0.63 [0.43-0.94], 0.35 [0.17-0.69], and 0.74 [0.57-0.95], respectively), while late-preterm birth (34-36 weeks) was associated with a 1.6-fold higher risk among females at 0-5 years, and a 1.4-fold risk among males at 5-10 years. Analyses on recurrent fractures showed a similar pattern. Children and young adults, in particular males, born extremely or very preterm may have fewer bone fractures; this is partly explained by severe medical conditions in this group.