Its cause may be due to an immature digestive system, or an immature nervous system, or perhaps something else. (dadsadventure.com)
WebMD states that it might be «the result of a baby's sensitive temperament and an immature nervous system.» (momtricks.com)
A premature baby has premature organs regulated by an immature nervous system, which can cause physiological stress responses to occur if the baby becomes overstimulated or disorganized in their behavior. (verywellfamily.com)