Trends in the incidence of severe retinopathy of prematurity in a geographically defined population over a 10-year period.

OBJECTIVE: To examine trends in the incidence of severe (> or =grade 3) retinopathy of prematurity (ROP) in infants with birth weight of < or =1250 g in a geographically defined population over a 10-year period. METHODS: An observational study was conducted of all infants who had a birth weight < or =1250 g and were born to mothers who were resident in the county of Leicestershire, United Kingdom, during the period January 1, 1990, to December 30, 1999. Cases were identified by the Trent Neonatal Survey. The incidence of severe ROP (> or =grade 3) was compared in 2 successive 5-year periods: 1990-1994 and 1995-1999. RESULTS: Comparing the first 5-year period (1990-1994) with the second (1995-1999), the total number of live births fell (60 789 vs 56 564). However, there was a significant increase in the number of births with birth weight < or =1250 g (including live and dead; 615 vs 734; live births only: 455 vs 556). Survival to 42 weeks of infants who were born at < or =1250 g was significantly better in the latter time period (203 vs 302; odds ratio [OR] for death: 0.54; 95% confidence interval [CI]: 0.39-0.75). The number of cases of severe ROP was 4 times higher during the second time period compared with the first (9 vs 36). A significantly increased risk for the development of severe ROP was seen during the second time period (OR: 2.92; 95% CI: 1.37-6.20). Even after allowing for the change in gestation induced by the improved survival during the second time period, the increased risk remained (OR: 2.81; 95% CI: 1.27-6.21). CONCLUSIONS: There is strong evidence that the incidence of severe ROP among infants with birth weight < or =1250 g increased in the latter half of the last decade. The increased risk seems to be independent of the increase in survival.