Birth weight–stratified analysis of retinopathy of prematurity: a single-center cohort including infants below 400 g

Background: This study aimed to clarify birth weight (BW)–specific ophthalmic outcomes of retinopathy of prematurity (ROP), including extremely rare survivors weighing < 400 g. Methods: This single-center retrospective cohort study included preterm infants with BW < 1800 g who were admitted to the neonatal intensive care unit or the growing care unit of the University of Tokyo Hospital between 2019 and 2024. Ophthalmic outcomes were followed until ROP regression. Infants were stratified into 200-g BW categories, and four outcomes were evaluated for each stratum: ROP incidence, ROP treatment rates, ROP severity, and in-hospital mortality. For comparison with previous reports, outcomes were also calculated for infants with BW < 1000 g. Results: Among 266 infants with ophthalmic follow-up, 132 infants (49.6%) developed ROP and 41 infants (15.4%) underwent treatment. ROP incidence increased with decreasing BW, reaching 100% among infants weighing < 600 g. Notably, the highest treatment rate was observed in the 400–599 g group (50.0%), whereas the < 400 g group showed a lower rate of 25.0%. Conversely, although the ROP incidence in infants weighing ≥ 1400 g was low (10 infants; 10.4%), there were still three infants who required treatment in this group (3.1%). Aggressive ROP occurred in six (2.3%) infants, four (13.3%) in 400–599 g and two (6.5%) in 800–999 g. Conclusion: This study provides detailed BW-specific ROP outcomes, including those of infants weighing < 400 g. Treatment rate in infants < 400 g may not increase uniformly with decreasing BW, suggesting distinct risk layers across strata.