Whereas ET1 is difficult to measure due to its short half-life, the precursor peptide C-terminal proendothelin-1 (CT-proET1) is far more stable and available for estimation of ET1 levels.12 As both ANP and ET1 are involved in retinal growth and angiogenesis, we intended to explore the role of their stable biomarkers for early prediction of subsequent development of ROP. Here, EDN1 is linked to retinopathy of prematurity.