Size and Growth After NICU Discharge in Extremely Low-Birth-Weight or Extremely Preterm Infants

Among extremely low-birth-weight (ELBW; <1000 g) or extremely preterm (EPT; <28 + 0 weeks) infants, we aimed to describe size indicators at 18 to 24 months of corrected age and growth from neonatal intensive care unit (NICU) discharge to follow-up and to examine infant and maternal determinants of those outcomes.

We studied 7301 ELBW/EPT children from 77 Vermont Oxford Network member hospitals. Continuous size indicators at 18 to 24 months were z scores of weight, length, head circumference, and body mass index based on World Health Organization standards. We represented growth by z score changes in weight and head circumference from NICU discharge to 18 to 24 months. We estimated associations of infant and maternal factors with indicators of size and growth in multivariate linear and logistic regression.

Median gestational age was 26 weeks and birth weight was 800 g. From NICU discharge to 18 to 24 months, weight increased by median 0.74 z scores, but at 18 to 24 months, ELBW/EPT children remained lighter than the reference (median z score -0.26). In adjusted analyses, small-for-gestational-age (SGA) status, NICU weight faltering, and surgical necrotizing enterocolitis all predicted more rapid weight gain after NICU discharge, but infants with those conditions remained smaller at 18 to 24 months. For example, SGA infants gained 0.44 z scores more weight after NICU discharge than non-SGA infants (95% CI, 0.34-0.54) but were nonetheless 0.95 z scores lighter at 18 to 24 months (95% CI, -1.05 to -0.86).

Our findings suggest substantial, albeit incomplete, catch-up growth in ELBW/EPT infants after NICU discharge through 18 to 24 months.