Generally, in the early stages of preterm infants, it is still necessary to feed them promptly with preterm formula. Since the gastrointestinal function of preterm infants is relatively weak, they may not be able to digest and absorb some full-term formula, which can easily increase the burden on the gastrointestinal tract. If the baby's development is currently good, you can switch to ordinary formula. During the transition between two formula brands, there should first be a gradual shift; you can start by mixing the two formulas, using more preterm formula and less ordinary formula. Gradually switch to the new ordinary formula brand, reducing the amount of preterm formula, allowing the baby to adapt gradually.