Timing of preterm infant fortification Post-discharge fortification of preterm infants refers to feeding with fortified breast milk, preterm formula, and post-discharge formula for preterm infants. According to the current principles of evidence-based medicine, post-discharge fortification can be applied until 3 months of corrected age to l year of corrected age. Clinicians can also make judgments based on the nutritional status of preterm infants and their physical developmental monitoring indicators including normal growth curves of weight, length, and head circumference during regular post-discharge follow-up, taking full account of individual differences. Timing of introduction of other foods There are individual differences in the age of introduction of other foods in preterm infants, which is related to their maturity level. The timing of introduction of other foods is relatively late in preterm births with small gestational age, generally not earlier than 4 months of corrected age and not later than 6 months of corrected age. Supplementation of other nutrients 1, vitamin D: According to China’s “Recommendations for the Prevention and Treatment of Vitamin D Deficiency Rickets”, premature/low birth weight infants should be supplemented with vitamin D 800-1000 U/d after birth, and 400 U/d after 3 months of age until 2 years of age. 2, iron: preterm / low birth weight infants with low iron reserves, 2 weeks after birth need to start supplementing elemental iron until the correction age of 1 year. This supplementation includes iron content in iron-fortified formula, breast milk fortification, food and iron preparations.