Growth at 2 years in children born preterm: donor milk versus preterm formula

The NICHD Neonatal Research Network MILK Trial randomized infants born preterm to receive donor milk or preterm formula. We hypothesized that there would be no growth differences at follow-up by study diet.

We conducted a secondary analysis of the double-blind trial of infants <29 weeks' gestation or <1000 g at birth at 15 US centers (September 2012-March 2019). Infants were randomized to receive donor milk or preterm formula. The primary outcome was body mass index (BMI) Z-score at 22-26 months corrected age.

Among 483 trial participants, 376 were seen at follow-up (181 donor milk, 195 formula). At 22-26 month follow-up, anthropometrics were similar for the two groups, including BMI Z-score (donor milk 0.21 ± 1.13, formula 0.23 ± 1.28, p = 0.67). There was a greater increase in weight Z-score between discharge and follow-up for children randomized to donor milk (donor milk 1.04 ± 1.28, formula 0.73 ± 1.30, p = 0.004).

While BMI Z-scores were similar at 22-26 months corrected age, patterns of growth between discharge and follow-up differed by study diet. Children fed donor milk in early infancy showed a greater increase in weight Z-score between discharge and follow-up than children fed preterm formula in early infancy.

At 2 years, the anthropometrics were similar for children randomized to donor milk or preterm formula in early infancy. Patterns of growth between discharge and follow-up differed by early infancy diet. There was a greater weight Z-score increase between discharge and follow-up for children randomized to donor milk than formula. Donor milk appears to be non-inferior to preterm formula with respect to growth at 2 years for children born extremely preterm. Policies and practices that facilitate parental milk provision and donor milk availability are needed for infants born extremely preterm.