Iron Malabsorption

In this phase II trial, the investigators overarching goal is to demonstrate the feasibility and potential benefit of darbepoetin (Darbe) plus slow-release intravenous (IV) iron to decrease transfusions, maintain iron sufficiency and improve the neurodevelopmental outcomes of preterm infants. Investigators hypothesize that in infants \< 32 completed weeks of gestation, combined treatment with Darbe plus Ferumoxytol (FMX) or Darbe plus low molecular weight iron dextran (LMW-ID) will: 1) be safe, 2) decrease or eliminate transfusions, 3) maintain iron sufficiency, 4) result in higher hematocrit and 5) improve neurodevelopment. Investigators further hypothesize that when compared to oral iron supplementation (standard care), IV iron will be better tolerated, with less effect on the gastrointestinal (GI) microbiome