Most cases of ROP were found in infants born at very low gestational age (<28 weeks at birth). With a preterm birth, an infant's retina is barely vascularized and has lower vascular endothelial growth factor (VEGF) and insulin growth factor 1 (IGF-1) levels than it should have in a case of full-term delivery. This evidence concerns the gene IGF1 and retinopathy of prematurity.