ROPScore predicts severe ROP assuming a specific cut off level that needs to be validated for each population. The score is calculated once per child at 2 or 6 weeks of life. The aim is to decrease the number of screened children and/or reduce the frequency of examinations in low risk infants. This process requires the following parameters: BW, GA, weight gain proportional to BW measured at the given week, the presence or absence of blood transfusion and oxygen in mechanical ventilation up to the analyzed week.