Hyperbilirubinemia in Full-term Neonates

Inclusion Criteria: * Term infants with 37 weeks ≤ gestational age \< 42 weeks and 2500g ≤ birth weight \< 4000g * Age ≤24 hours * Stable basic vital signs * Liver and kidney function normal * No prior use of antibiotics or ecological agents before specimen collection * Healthy mothers during pregnancy, with no history of antibiotics or microecological agents before, during, or after childbirth * Exclusively breastfed * Informed consent provided voluntarily. Exclusion Criteria: * Gestational age \<37 weeks or ≥42 weeks * Complications present with pneumonia, septicemia, or other illness * Severe immunodeficiency disease present * Inherited metabolic diseases identified * Congenital biliary malformations or other organ malformations * Drug allergies * History of asphyxiation * Before enteral feeding, constipation, abdominal distension, diarrhea, vomiting or other gastrointestinal symptoms had appeared * Enteral feeding was not performed * Antibiotics or other microecological agents were used * Isoimmune hemolysis, extravascular hemolysis, polycythemia, erythrocyte enzyme deficiency, erythrocyte morphological abnormality, hemoglobinopathy, etc. * Hyperbilirubinemia were diagnosed within 24 hours of birth * Situations that may warrant exclusion as determined by the researcher, such as a guardian with mental illness or frequent changes in living or working environments, which might result in loss of follow-up