OBJECTIVETo investigate the factors involved in the development of retinopathy of prematurity (ROP), and to provide the preliminary data for the evaluation of current criteria for ROP screening.

METHODPremature infants with birth body weight (BBW) ≤ 2000 g or gestational age (GA) ≤ 34 weeks in the two hospitals in Zhejiang between March 2005 and November 2008 were recruited and examined by indirect ophthalmoscopy. The records were analyzed.

RESULTOne thousand two hundred and twenty-five premature infants were included. Of them, 713 were male and 512 female. There were 179 twins and 21 triplets in the premature infants. The incidence of ROP was 10.8% (132 in 1225 patients). There were 12 cases (0.98%) to the point of pre threshold ROP. 4 cases (0.3%) developed threshold ROP. Only one case developed pre threshold ROP of low risk among 65 cases without history of oxygen treatment (1.5%). The percentage has significant difference compared to that of cases with history of oxygen (χ(2) = 5.115, P < 0.01).Between ROP and Non-ROP groups, there was significant difference in BBW(F = 26.39, P < 0.001), gestational age (F = 19.73, P < 0.001), but there was no significant difference in sex (χ(2) = 0.279, P > 0.05) or twins and triplets (χ(2) = 3.449, P > 0.05). The incidence of ROP among premature infants with BBW ≤ 1000 g was more than three times of that with BBW > 1000 g, and the incidence of ROP among premature infants with GA ≤ 28 weeks was about 2.5 times of that with GA > 28 weeks. Logistic regression analysis indicated that less BBW or shorter GA or undulation of blood oxygen concentration was a significant risk factor involved in the development of ROP (r = 0.57, P < 0.05). All ROP patients were cured.

CONCLUSIONLess BBW, shorter GA and undulation of blood oxygen concentration are the important risk factors for the development of ROP. Premature infants with BBW ≤ 1000 g or GA ≤ 28 weeks, who had oxygen history, should be given very special attention in the ROP screening. The current criteria for ROP screening should be narrowed. In general, the ROP screening has lowered the incidence of blindness among children by investigating and treating ROP timely.