A low concentration of IGF-1 is related to the subsequent progression of severe ROP, so it is a risk predictor (56, 58). In addition, the early return of IGF-1 to normal levels in premature infants can prevent ROP (59). The critical time for the detection of serum IGF-1 is in the third week after delivery (57). This evidence concerns the gene IGF1 and retinopathy of prematurity.