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 retrospective single-center cohort study included preterm infants with BW < 1800 g who were admitted to the neonatal intensive 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%, 95%CI 43.5–55.8) developed ROP and 41 infants (15.4%, 95%CI 11.3–20.3) underwent treatment. ROP incidence and treatment rates showed significant inverse trends across ordered BW strata (both Cochran–Armitage trend test, P < 0.001). ROP incidence reached 100% (95%CI 90.7–100.0) among infants weighing < 600 g. Treatment rates were 50.0% (95%CI 31.3–68.7) in the 400–599 g group and 25.0% (95%CI 3.2–65.1) in the < 400 g group. Conclusion This study provides detailed BW-specific ROP outcomes, including those of infants weighing < 400 g. ROP incidence and treatment rates showed significant inverse trends across decreasing BW strata. Given the retrospective single-center design, the descriptive nature of the study, and the limited number of infants in the < 400 g group, the results should be interpreted cautiously and considered hypothesis-generating.