Echocardiographic characteristics of the study population, median (IQR).

(): Data only for patients with constrictive ductus; V. ductus, Maximal ductal flow velocity; LPAV, Mean left pulmonary artery flow velocity; EDLPAV, End diastolic left pulmonary artery flow velocity; LA/Ao, Left atria-to-Aorta diameter ratio; IQR, Interquartile interval; T1, the day of diagnosis by echocardiography; T2, the day after the end of treatment with ibuprofen. For patients in the Control group, T1: 1–3 day of life and T2: 4–6 days of life; paired comparison T1 vs T2 in the same infants, (*): p<0.05, (**): p<0.01.