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

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.

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.

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.

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.

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