Neonatal complications arise from the complex interplay between gestational maturity, birth-related physiological stress, and the immature organ systems of the newborn. Hyperbilirubinemia results from increased red blood cell turnover (shorter neonatal RBC lifespan of 70-90 days), immature hepatic conjugation enzymes (UDP-glucuronosyltransferase), and enhanced enterohepatic circulation. Unconjugated bilirubin is neurotoxic and can cross the blood-brain barrier, causing kernicterus with permanent neurological damage including cerebral palsy, sensorineural hearing loss, and cognitive impairment. Neonatal sepsis — caused primarily by Group B Streptococcus, E. coli, and Listeria — presents with subtle, nonspecific signs due to the immature immune system's limited inflammatory response.