The study’s goal was to evaluate the intestinal microbiota of VLBW infants who received different enteral iron supplementation (EIS) levels. A prospective study collected longitudinal stool samples from 80 VLBW newborns up to 2 months postnatally. Microbiome compositions were calculated using the 16S rRNA regions V4, and bacterial functional predictions were made using the Piphillin programme. To investigate the associations between initial EIS dosage and stool microbiota and bacterial functional potential, linear mixed effect models and Wilcoxon rank-sum tests were used. There were 105 samples obtained before EIS began and 237 samples obtained after EIS began from newborns with birth gestational age and weight of 28.1 ± 2.4 weeks and 1103± 210 g, respectively. The average postnatal age when EIS was started was 17.9+ 6.9 days, and the average initial EIS dose was 4.8 ±1.1 mg kg1 day1. Infants given 6 mg kg1 day1 had larger abundances of Proteus and Bifidobacterium and lower alpha diversity than those given lower doses.

Higher EIS dosage is associated with higher Proteus and Bifidobacterium abundances, a less diversified microbiome, and a higher anticipated likelihood for bacterial epithelial invasion. These observational data should be investigated further in a randomised trial to determine the appropriate dosage of EIS in VLBW newborns.