Retinopathy of prematurity in discordant twins: is the small twin at increased risk?

Purpose: To examine the effect of birth weight (BW) independent of gestational age (GA) on Retinopathy of prematurity (ROP) in preterm discordant twins. Methods: A retrospective cohort study of 45 preterm twin pairs born at < 34 weeks of gestation with BW discordance of ≥ 20%. The twin pairs were divided into two groups based on BW – small or large. Rates of ROP, stage, treatment, and prognosis were compared between the two groups. Other neonatal outcomes related to prematurity were also compared between groups. Results: The mean gestation age at delivery was 31.1 weeks of gestation. The rate of ROP was significantly higher among the smaller twins compared to the larger twins (8.9% vs 0% respectively, p = 0.04). All smaller twins with ROP had stage 2 disease, and all cases of ROP had resolved without treatment. Regarding neonatal morbidities, the smaller twins had longer hospitalization length (53.8 vs 39.4 days respectively, p < 0.01) and a higher rate of hypoglycemia (55.6% vs 24.4% respectively, p = 0.003), whereas the larger twins were more commonly affected by respiratory distress syndrome (59.1% vs 26.7% respectively, p = 0.002). Conclusion: The rate of ROP was higher among the small twins in preterm discordant twins. This may indicate that low BW rather than early GA is the main factor contributing to the development of ROP.