Chilean reference of length at birth

Background: To generate a reference of length at birth (LB) according to sex and gestational age (GA) of the Chilean population.

Methods: This cross-sectional observational study used public pooled Chilean newborn (NB) population data registered by the Civil Registry and Identification Service in Chile from 2000 to 2016. Multiple births, entries without information for LB, GA, and sex, and birth lengths <-4SD and > 4SD, were excluded. After applying the selection and randomization criteria, the final sample was made up of 5 010 963 NB (2 560 310 boys; 2 450 653 girls). Length at birth centiles by sex and GA (24-42 weeks) were calculated using the GAMLSS method and then compared with the INTERGROWTH-21st standard.

Results: Girls had a lower LB than boys. For most GA and in both sexes, the absolute and percentage differences of percentiles as compared with INTERGROWTH-21st were lower than 1 cm and 1%, respectively.

Conclusions: We present a reference for LB by sex and GA in the Chilean population, developed following updated methodological criteria for neonatal anthropometry, which is acceptably consistent with the INTERGROWTH-21st standard. The reference we propose may be used in clinical and epidemiological studies to identify either Chilean individuals or populations, respectively, at higher risk of perinatal and infant adverse events related to LB.