Z1: Discriminant probability formula for ROP occurrence = 8.483 − 0.1699 × GA − 0.003125 × BW − 0.071678 × CRP + 0.003203 × α1AG + 0.0141 × HP (Z1 ≥ 0 indicates ROP occurrence, Z1 < 0 indicates no occurrence);. Here, CRP is linked to retinopathy of prematurity.