The relationship between discordant birth weight in twin pairs and the development of retinopathy of prematurity.

The association of low birth weight and development of retinopathy of prematurity (ROP) is well established for singletons; however, the association of birth weight and ROP in twins of discordant weight is understudied. Using an ROP registry, we investigated whether smaller twins were at greater risk for developing any stage ROP (stage 1 or greater in either eye) compared with their larger siblings, after adjusting for birth weight and gestational age. Discordance was defined as a birth weight difference of >25%. In a cohort of 2,083 infants (2006-2021), 36 discordant twin pairs were identified. The smaller twin had an increased odds of developing any ROP (OR = 2.7; 95% CI, 1.3-5.9; P = 0.01) compared with the larger sibling. This relationship was no longer significant following adjustment for gestational age and birth weight (adjusted OR = 0.92; CI, 0.11-7.43; P = 0.94). The results suggest that although the smaller twins in discordant pairs are at an increased risk of any stage ROP, this risk is driven by low birth weight conditional on gestational age.