Flow chart showing the patient recruitment.

Recruiting centers and recruitment periods are shown on the top row. Recruitment periods vary between hospitals due the existence of other studies recruiting the same type of patients. *One other study also aimed to recruit the same type of patients during this period. **During this two year period there were some interruptions in the recruitment due to circumstances not related with the study. ***It includes patients that did not meet inclusion criteria (3) and patients whose parents denied participation (11).