GPT and retinopathy of prematurity: AHS: abnormal hearing screening; ALT: alanine aminotransferase; AST: aspartate aminotransferase; BPD: bronchopulmonary dysplasia; CMV: cytomegalovirus; GGT: gamma-glutamyl transferase; IVH: intraventricular hemorrhage; NEC: necrotizing enterocolitis; RDS: respiratory distress syndrome; ROP: retinopathy of prematurity