Incidence of retinopathy of prematurity in infants born before 27 weeks' gestation in Sweden.

Objective: To determine the incidence of retinopathy of prematurity (ROP) in extremely preterm infants born before 27 weeks' gestation in Sweden during a 3-year period.

Methods: A national, prospective, population-based study was performed in Sweden from April 1, 2004, to March 31, 2007. The ophthalmologic part of the study was separately organized, and screening for ROP was performed beginning postnatal week 5. The criteria for the treatment of ROP agreed with the recommendations of the Early Treatment for Retinopathy of Prematurity Cooperative Group.

Results: During the study, 506 of 707 live-born infants survived until the first eye examination. Of these, 368 (72.7%) had ROP: 37.9% had mild ROP and 34.8% had severe ROP. Ninety-nine infants (19.6%) were treated. Gestational age at birth was a stronger predictor of ROP than was birth weight. A log-linear relationship between severe ROP and gestational age at birth was found in the present cohort, and the risk of ROP was reduced by 50% for each week of increase in gestational age at birth.

Conclusions: Today, extremely preterm infants are surviving, and this population-based study with ROP as a primary outcome shows a higher incidence of this condition than in previously reported national cohorts.