Postnatal growth in small vulnerable newborns: A longitudinal study of 2 million Brazilians using routine register-based linked data.

BACKGROUND: Preterm, low birth weight (LBW) and small for gestational age (SGA) newborns have a higher frequency of adverse health outcomes, including linear and ponderal growth impairment.

OBJECTIVE: To describe the growth trajectories and to estimate catch-up growth during the first five years of life of small newborns according to three vulnerability phenotypes (preterm, LBW, SGA).

METHODS: Longitudinal study using linked data from the 100 Million Brazilian Cohort baseline, the Brazilian National Live Birth System (SINASC), and the Food and Nutrition Surveillance System (SISVAN) from 2011 to 2017. We estimated the length/height-for-age (L/HAZ) and weight-for-age z-scores (WAZ) trajectories from children of 6 to 59 months using the linear mixed model for each vulnerable newborn phenotype. Growth velocity for both L/HAZ and weight-for-age WAZ was calculated considering the change (Δ) in the mean z-score between two-time points. Catch-up growth was defined as a change in z-score >0.67 at any time during follow-up.

RESULTS: 2,021,998 live born children and 8,726,599 observations were analyzed. The prevalence of at least one of the vulnerable phenotypes was 16.7% and 0.6% were simultaneously preterm, LBW, and SGA. For those born at term, all phenotypes had a period of growth recovery from 12 months. For preterm infants, the onset of L/HAZ growth recovery started later at 24 months and the growth trajectories appear to be lower than those born at term, a condition aggravated among children with the 3 phenotypes. Preterm and female infants seem to experience slower growth recovery than those born at term and males. The catch-up growth occurs at 24-59 months for males preterm: preterm+AGA+NBW (Δ=0.80), preterm+AGA+LBW (Δ=0.88), and preterm+SGA+LBW (Δ=1.088); and among females: term+SGA+NBW (Δ=0.69), term+AGA+LBW (Δ=0.72), term+SGA+LBW (Δ=0.77), preterm+AGA+LBW (Δ=0.68) and preterm+SGA+LBW (Δ=0.83).

CONCLUSIONS: Children born preterm seem to reach L/HAZ and WAZ growth trajectories lower than those attained by children born at term, a condition aggravated among the most vulnerable.