Diet, weight gain, and head growth in hospitalized US very preterm infants: a 10-year observational study

Background: The benefits of human milk for hospitalized preterm infants are well documented, but the extent to which current human milk diets adequately support growth is uncertain.

Objectives: 1) To quantify differences in weight gain and head growth between very preterm infants fed human milk compared with infant formula; and 2) to describe trends in the magnitude of these differences over time.

Methods: We studied infants from 777 US NICUs in the Vermont Oxford Network database. We included all surviving infants 23-29 weeks of gestation or 401-1500 g birth weight (maximum gestational age 32 wk) and excluded infants discharged >42 weeks of gestation or with congenital anomalies. In diet-growth analyses, we included infants born 2012-2016 (n = 138,703) to reflect current practice. In trend analyses, we included a 10-y cohort (n = 263,367). We categorized diet at NICU discharge/transfer as: 1) human milk only (no formula or fortifier); 2) human milk with formula or fortifier (mixed); or 3) infant formula only. Outcomes were weight and head circumference z-score change from birth to discharge relative to a fetal reference.

Results: Diet at discharge/transfer was human milk only for 18,274 (6.6%), mixed for 121,621 (44%), and formula only for 137,067 (49%). Weight deviated more from the fetal reference for infants fed both human milk diets compared with formula only (weight z-score change for infants fed human milk only, -0.88; mixed, -0.82; formula only -0.80; P < 0.0001 for diet overall). There were also differences by diet in head z-score change (human milk only, -0.52; mixed, -0.49; formula only, -0.45; P < 0.0001 for diet overall). The magnitude of these differences has diminished substantially over 10 y.

Conclusions: Very preterm infants receiving human milk compared with infant formula diets have a slower weight gain and head growth at hospital discharge.