APLN and retinopathy of prematurity: Our study found that preterm infants with a gestational age of < 32 weeks and birth weight of < 1500 g had higher plasma VEGF levels and lower plasma apelin-13 levels in infants with ROP than those in infants without ROP at 4–6 weeks after birth; and infants with severe ROP had higher plasma VEGF levels and lower plasma apelin-13 levels than infants with wild ROP.